seconds of code

Curated collection of useful Javascript snippets that you can understand in 30 seconds or less.

Use Ctrl + F or command + F to search for a snippet.
Contributions welcome, please read the contribution guide.
Snippets are written in ES6, use the Babel transpiler to ensure backwards-compatibility.

Array concatenation
Array difference
Array intersection
Array union
Average of array of numbers
Chunk array
Compact
Count occurrences of a value in array
Deep flatten array
Drop elements in array
Fill array
Filter out non unique values in an array
Flatten array up to depth
Flatten array
Get max value from array
Get min value from array
Group by
Head of list
Initial of list
Initialize array with range
Initialize array with values
Last of list
Median of array of numbers
Nth element of array
Pick
Shuffle array
Similarity between arrays
Sum of array of numbers
Tail of list
Take
Unique values of array

Array

Array concatenation

拼接

Use Array.concat() to concatenate an array with any additional arrays and/or values, specified in args.
ES6

const arrayConcat = (arr, ...args) => arr.concat(...args);
// arrayConcat([1], 2, [3], [[4]]) -> [1,2,3,[4]]

ES5

var arrayConcat = function arrayConcat(arr) {
  for (var _len = arguments.length, args = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
    args[_key - 1] = arguments[_key];
  }

  return arr.concat.apply(arr, args);
};
// arrayConcat([1], 2, [3], [[4]]) -> [1,2,3,[4]]

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Array difference

差异

Create a Set from b, then use Array.filter() on a to only keep values not contained in b.
ES6

const difference = (a, b) => { const s = new Set(b); return a.filter(x => !s.has(x)); };
// difference([1,2,3], [1,2]) -> [3]

ES5

var difference = function difference(a, b) {
  var s = new Set(b);return a.filter(function (x) {
    return !s.has(x);
  });
};
// difference([1,2,3], [1,2]) -> [3]

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Array intersection

交叉

Create a Set from b, then use Array.filter() on a to only keep values contained in b.
ES6

const intersection = (a, b) => { const s = new Set(b); return a.filter(x => s.has(x)); };
// intersection([1,2,3], [4,3,2]) -> [2,3]

ES5

var intersection = function intersection(a, b) {
  var s = new Set(b);return a.filter(function (x) {
    return s.has(x);
  });
};
// intersection([1,2,3], [4,3,2]) -> [2,3]

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Array union

联合

Create a Set with all values of a and b and convert to an array.
ES6

const union = (a, b) => Array.from(new Set([...a, ...b]));
// union([1,2,3], [4,3,2]) -> [1,2,3,4]

ES5

function _toConsumableArray(arr) {
  if (Array.isArray(arr)) {
    for (var i = 0, arr2 = Array(arr.length); i < arr.length; i++) {
      arr2[i] = arr[i];
    }
    return arr2;
  } else {
    return Array.from(arr);
  }
}

var union = function union(a, b) {
  return Array.from(
    new Set([].concat(_toConsumableArray(a), _toConsumableArray(b)))
  );
};
// union([1,2,3], [4,3,2]) -> [1,2,3,4]

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Average of array of numbers

平均

Use Array.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.
ES6

const average = arr => arr.reduce((acc, val) => acc + val, 0) / arr.length;
// average([1,2,3]) -> 2

ES5

var average = function average(arr) {
  return (
    arr.reduce(function(acc, val) {
      return acc + val;
    }, 0) / arr.length
  );
};
// average([1,2,3]) -> 2

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Chunk array

重组整列

Use Array.from() to create a new array, that fits the number of chunks that will be produced. Use Array.slice() to map each element of the new array to a chunk the length of size. If the original array can't be split evenly, the final chunk will contain the remaining elements.
ES6

const chunk = (arr, size) =>
  Array.from({length: Math.ceil(arr.length / size)}, (v, i) => arr.slice(i * size, i * size + size));
// chunk([1,2,3,4,5], 2) -> [[1,2],[3,4],5]

ES5

var chunk = function chunk(arr, size) {
  return Array.from({ length: Math.ceil(arr.length / size) }, function(v, i) {
    return arr.slice(i * size, i * size + size);
  });
};

// chunk([1,2,3,4,5], 2) -> [[1,2],[3,4],5]

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Compact

有效值

Use Array.filter() to filter out falsey values (false, null, 0, "", undefined, and NaN).
ES6

const compact = (arr) => arr.filter(v => v);
// compact([0, 1, false, 2, '', 3, 'a', 'e'*23, NaN, 's', 34]) -> [ 1, 2, 3, 'a', 's', 34 ]

ES5

var compact = function compact(arr) {
  return arr.filter(function(v) {
    return v;
  });
};
// compact([0, 1, false, 2, '', 3, 'a', 'e'*23, NaN, 's', 34]) -> [ 1, 2, 3, 'a', 's', 34 ]

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Count occurrences of a value in array

存在总数

Use Array.reduce() to increment a counter each time you encounter the specific value inside the array.
ES6

const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);
// countOccurrences([1,1,2,1,2,3], 1) -> 3

ES5

const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);
// countOccurrences([1,1,2,1,2,3], 1) -> 3

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Deep flatten array

深平阵数组

Use recursion. Use Array.reduce() to get all elements that are not arrays, flatten each element that is an array.
ES6

const deepFlatten = arr =>
  arr.reduce((a, v) => a.concat(Array.isArray(v) ? deepFlatten(v) : v), []);
// deepFlatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]

ES5

var deepFlatten = function deepFlatten(arr) {
  return arr.reduce(function(a, v) {
    return a.concat(Array.isArray(v) ? deepFlatten(v) : v);
  }, []);
};
// deepFlatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]

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Drop elements in array

提取条件项

Loop through the array, using Array.shift() to drop the first element of the array until the returned value from the function is true. Returns the remaining elements.
ES6

const dropElements = (arr, func) => {
  while (arr.length > 0 && !func(arr[0])) arr.shift();
  return arr;
};
// dropElements([1, 2, 3, 4], n => n >= 3) -> [3,4]

ES5

var dropElements = function dropElements(arr, func) {
  while (arr.length > 0 && !func(arr[0])) {
    arr.shift();
  }
  return arr;
};
// dropElements([1, 2, 3, 4], n => n >= 3) -> [3,4]

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Fill array

Use Array.map() to map values between start (inclusive) and end (exclusive) to value. Omit start to start at the first element and/or end to finish at the last.

ES6

const fillArray = (arr, value, start = 0, end = arr.length) =>
  arr.map((v, i) => i >= start && i < end ? value : v);
// fillArray([1,2,3,4],'8',1,3) -> [1,'8','8',4]

ES5

var fillArray = function fillArray(arr, value) {
  var start =
    arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : 0;
  var end =
    arguments.length > 3 && arguments[3] !== undefined
      ? arguments[3]
      : arr.length;
  return arr.map(function(v, i) {
    return i >= start && i < end ? value : v;
  });
};
// fillArray([1,2,3,4],'8',1,3) -> [1,'8','8',4]

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Filter out non-unique values in an array

Use Array.filter() for an array containing only the unique values.

ES6

const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
// filterNonUnique([1,2,2,3,4,4,5]) -> [1,3,5]

ES5

var filterNonUnique = function filterNonUnique(arr) {
  return arr.filter(function(i) {
    return arr.indexOf(i) === arr.lastIndexOf(i);
  });
};
// filterNonUnique([1,2,2,3,4,4,5]) -> [1,3,5]

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Flatten array up to depth

Use recursion, decrementing depth by 1 for each level of depth. Use Array.reduce() and Array.concat() to merge elements or arrays. Base case, for depth equal to 1 stops recursion. Omit the second element, depth to flatten only to a depth of 1 (single flatten).

ES6

const flattenDepth = (arr, depth = 1) =>
  depth != 1 ? arr.reduce((a, v) => a.concat(Array.isArray(v) ? flattenDepth(v, depth - 1) : v), [])
  : arr.reduce((a, v) => a.concat(v), []);
// flattenDepth([1,[2],[[[3],4],5]], 2) -> [1,2,[3],4,5]

ES5

var flattenDepth = function flattenDepth(arr) {
  var depth =
    arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 1;
  return depth != 1
    ? arr.reduce(function(a, v) {
        return a.concat(Array.isArray(v) ? flattenDepth(v, depth - 1) : v);
      }, [])
    : arr.reduce(function(a, v) {
        return a.concat(v);
      }, []);
};
// flattenDepth([1,[2],[[[3],4],5]], 2) -> [1,2,[3],4,5]

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Flatten array

Use Array.reduce() to get all elements inside the array and concat() to flatten them.

ES6

const flatten = arr => arr.reduce((a, v) => a.concat(v), []);
// flatten([1,[2],3,4]) -> [1,2,3,4]

ES5

var flatten = function flatten(arr) {
  return arr.reduce(function(a, v) {
    return a.concat(v);
  }, []);
};

// flatten([1,[2],3,4]) -> [1,2,3,4]

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Get max value from array

Use Math.max() combined with the spread operator (...) to get the maximum value in the array.

ES6

const arrayMax = arr => Math.max(...arr);
// arrayMax([10, 1, 5]) -> 10

ES5

function _toConsumableArray(arr) {
  if (Array.isArray(arr)) {
    for (var i = 0, arr2 = Array(arr.length); i < arr.length; i++) {
      arr2[i] = arr[i];
    }
    return arr2;
  } else {
    return Array.from(arr);
  }
}

var arrayMax = function arrayMax(arr) {
  return Math.max.apply(Math, _toConsumableArray(arr));
};
// arrayMax([10, 1, 5]) -> 10

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Get min value from array

Use Math.min() combined with the spread operator (...) to get the minimum value in the array.

ES6

const arrayMin = arr => Math.min(...arr);
// arrayMin([10, 1, 5]) -> 1

ES5

function _toConsumableArray(arr) {
  if (Array.isArray(arr)) {
    for (var i = 0, arr2 = Array(arr.length); i < arr.length; i++) {
      arr2[i] = arr[i];
    }
    return arr2;
  } else {
    return Array.from(arr);
  }
}

var arrayMin = function arrayMin(arr) {
  return Math.min.apply(Math, _toConsumableArray(arr));
};
// arrayMin([10, 1, 5]) -> 1

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Group by

Use Array.map() to map the values of an array to a function or property name. Use Array.reduce() to create an object, where the keys are produced from the mapped results.

ES6

const groupBy = (arr, func) =>
  arr.map(typeof func === 'function' ? func : val => val[func]<
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    .reduce((acc, val, i) => { acc[val] = (acc[val] || []).concat(arr[i]); return acc; }, {});
// groupBy([6.1, 4.2, 6.3], Math.floor) -> {4: [4.2], 6: [6.1, 6.3]}
// groupBy(['one', 'two', 'three'], 'length') -> {3: ['one', 'two'], 5: ['three']}

ES5

var groupBy = function groupBy(arr, func) {
  return arr
    .map(
      typeof func === "function"
        ? func
        : function(val) {
            return val[func];
          }
    )
    .reduce(function(acc, val, i) {
      acc[val] = (acc[val] || []).concat(arr[i]);
      return acc;
    }, {});
};
// groupBy([6.1, 4.2, 6.3], Math.floor) -> {4: [4.2], 6: [6.1, 6.3]}
// groupBy(['one', 'two', 'three'], 'length') -> {3: ['one', 'two'], 5: ['three']}

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Head of list

Use arr[0] to return the first element of the passed array.

ES6

const head = arr => arr[0];
// head([1,2,3]) -> 1

ES5

var head = function head(arr) {
  return arr[0];
};
// head([1,2,3]) -> 1

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Initial of list

Use arr.slice(0,-1)to return all but the last element of the array.

ES6

const initial = arr => arr.slice(0, -1);
// initial([1,2,3]) -> [1,2]

ES5

var initial = function initial(arr) {
  return arr.slice(0, -1);
};
// initial([1,2,3]) -> [1,2]

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Initialize array with range

Use Array(end-start) to create an array of the desired length, Array.map() to fill with the desired values in a range. You can omit start to use a default value of 0.

ES6

const initializeArrayRange = (end, start = 0) =>
  Array.apply(null, Array(end - start)).map((v, i) => i + start);
// initializeArrayRange(5) -> [0,1,2,3,4]

ES5

var initializeArrayRange = function initializeArrayRange(end) {
  var start =
    arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 0;
  return Array.apply(null, Array(end - start)).map(function(v, i) {
    return i + start;
  });
};
// initializeArrayRange(5) -> [0,1,2,3,4]

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Initialize array with values

Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values. You can omit value to use a default value of 0.

ES6

const initializeArray = (n, value = 0) => Array(n).fill(value);
// initializeArray(5, 2) -> [2,2,2,2,2]

ES5

var initializeArray = function initializeArray(n) {
  var value =
    arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 0;
  return Array(n).fill(value);
};
// initializeArray(5, 2) -> [2,2,2,2,2]

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Last of list

Use arr.slice(-1)[0] to get the last element of the given array.

ES6

const last = arr => arr.slice(-1)[0];
// last([1,2,3]) -> 3

ES5

var last = function last(arr) {
  return arr.slice(-1)[0];
};
// last([1,2,3]) -> 3

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Median of array of numbers

Find the middle of the array, use Array.sort() to sort the values. Return the number at the midpoint if length is odd, otherwise the average of the two middle numbers.

ES6

const median = arr => {
  const mid = Math.floor(arr.length / 2), nums = arr.sort((a, b) => a - b);
  return arr.length % 2 !== 0 ? nums[mid] : (nums[mid - 1] + nums[mid]) / 2;
};
// median([5,6,50,1,-5]) -> 5
// median([0,10,-2,7]) -> 3.5

ES5

var median = function median(arr) {
  var mid = Math.floor(arr.length / 2),
    nums = arr.sort(function(a, b) {
      return a - b;
    });
  return arr.length % 2 !== 0 ? nums[mid] : (nums[mid - 1] + nums[mid]) / 2;
};
// median([5,6,50,1,-5]) -> 5
// median([0,10,-2,7]) -> 3.5

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Nth element of array

Use Array.slice() to get an array containing the nth element at the first place. If the index is out of bounds, return []. Omit the second argument, n, to get the first element of the array.

ES6

const nth = (arr, n=0) => (n>0? arr.slice(n,n+1) : arr.slice(n))[0];
// nth(['a','b','c'],1) -> 'b'
// nth(['a','b','b']-2) -> 'a'

ES5

var nth = function nth(arr) {
  var n = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 0;
  return (n > 0 ? arr.slice(n, n + 1) : arr.slice(n))[0];
};
// nth(['a','b','c'],1) -> 'b'
// nth(['a','b','b']-2) -> 'a'

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Pick

Use Array.reduce() to convert the filtered/picked keys back to a object with the corresponding key:value pair if the key exist in the obj.

ES6

const pick = (obj, arr) =>
  arr.reduce((acc, curr) => (curr in obj && (acc[curr] = obj[curr]), acc), {});
// pick({ 'a': 1, 'b': '2', 'c': 3 }, ['a', 'c']) -> { 'a': 1, 'c': 3 }
// pick(object, ['a', 'c'])['a'] -> 1

ES5

var pick = function pick(obj, arr) {
  return arr.reduce(function(acc, curr) {
    return curr in obj && (acc[curr] = obj[curr]), acc;
  }, {});
};
// pick({ 'a': 1, 'b': '2', 'c': 3 }, ['a', 'c']) -> { 'a': 1, 'c': 3 }
// pick(object, ['a', 'c'])['a'] -> 1

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Shuffle array

Use Array.sort() to reorder elements, using Math.random() in the comparator.

ES6

const shuffle = arr => arr.sort(() => Math.random() - 0.5);
// shuffle([1,2,3]) -> [2,3,1]

ES5

var shuffle = function shuffle(arr) {
  return arr.sort(function() {
    return Math.random() - 0.5;
  });
};
// shuffle([1,2,3]) -> [2,3,1]

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Similarity between arrays

Use filter() to remove values that are not part of values, determined using includes().

ES6

const similarity = (arr, values) => arr.filter(v => values.includes(v));
// similarity([1,2,3], [1,2,4]) -> [1,2]

ES5

var similarity = function similarity(arr, values) {
  return arr.filter(function(v) {
    return values.includes(v);
  });
};
// similarity([1,2,3], [1,2,4]) -> [1,2]

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Sum of array of numbers

Use Array.reduce() to add each value to an accumulator, initialized with a value of 0.

ES6

const sum = arr => arr.reduce((acc, val) => acc + val, 0);
// sum([1,2,3,4]) -> 10

ES5

var sum = function sum(arr) {
  return arr.reduce(function(acc, val) {
    return acc + val;
  }, 0);
};
// sum([1,2,3,4]) -> 10

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Tail of list

Return arr.slice(1) if the array's length is more than 1, otherwise return the whole array.

ES6

const tail = arr => arr.length > 1 ? arr.slice(1) : arr;
// tail([1,2,3]) -> [2,3]
// tail([1]) -> [1]

ES5

var tail = function tail(arr) {
  return arr.length > 1 ? arr.slice(1) : arr;
};
// tail([1,2,3]) -> [2,3]
// tail([1]) -> [1]

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Take

Use Array.slice() to create a slice of the array with n elements taken from the beginning.

ES6

const take = (arr, n = 1) => arr.slice(0, n);
// take([1, 2, 3], 5) -> [1, 2, 3]
// take([1, 2, 3], 0) -> []

ES5

var take = function take(arr) {
  var n = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 1;
  return arr.slice(0, n);
};
// take([1, 2, 3], 5) -> [1, 2, 3]
// take([1, 2, 3], 0) -> []

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Unique values of array

Use ES6 Set and the ...rest operator to discard all duplicated values.

ES6

const unique = arr => [...new Set(arr)];
// unique([1,2,2,3,4,4,5]) -> [1,2,3,4,5]

ES5

function _toConsumableArray(arr) {
  if (Array.isArray(arr)) {
    for (var i = 0, arr2 = Array(arr.length); i < arr.length; i++) {
      arr2[i] = arr[i];
    }
    return arr2;
  } else {
    return Array.from(arr);
  }
}

var unique = function unique(arr) {
  return [].concat(_toConsumableArray(new Set(
10000
arr)));
};
// unique([1,2,2,3,4,4,5]) -> [1,2,3,4,5]

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Browser

Bottom visible

Use scrollY, scrollHeight and clientHeight to determine if the bottom of the page is visible.

ES6

const bottomVisible = _ =>
  document.documentElement.clientHeight + window.scrollY >= document.documentElement.scrollHeight || document.documentElement.clientHeight;
// bottomVisible() -> true

ES5

var bottomVisible = function bottomVisible(_) {
  return (
    document.documentElement.clientHeight + window.scrollY >=
      document.documentElement.scrollHeight ||
    document.documentElement.clientHeight
  );
};
// bottomVisible() -> true

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Current URL

Use window.location.href to get current URL.

ES6

const currentUrl = _ => window.location.href;
// currentUrl() -> 'https://google.com'

ES5

var currentUrl = function currentUrl(_) {
  return window.location.href;
};
// currentUrl() -> 'https://google.com'

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Element is visible in viewport

Use Element.getBoundingClientRect() and the window.inner(Width|Height) values to determine if a given element is visible in the viewport. Omit the second argument to determine if the element is entirely visible, or specify true to determine if it is partially visible.

ES6

const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
  const { top, left, bottom, right } = el.getBoundingClientRect();
  return partiallyVisible
    ? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) &&
      ((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
    : top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};
// e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
// elementIsVisibleInViewport(el) -> false (not fully visible)
// elementIsVisibleInViewport(el, true) -> true (partially visible)

ES5

var elementIsVisibleInViewport = function elementIsVisibleInViewport(el) {
  var partiallyVisible =
    arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : false;

  var _el$getBoundingClient = el.getBoundingClientRect(),
    top = _el$getBoundingClient.top,
    left = _el$getBoundingClient.left,
    bottom = _el$getBoundingClient.bottom,
    right = _el$getBoundingClient.right;

  return partiallyVisible
    ? ((top > 0 && top < innerHeight) ||
        (bottom > 0 && bottom < innerHeight)) &&
      ((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
    : top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};
// e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
// elementIsVisibleInViewport(el) -> false (not fully visible)
// elementIsVisibleInViewport(el, true) -> true (partially visible)

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Get scroll position

Use pageXOffset and pageYOffset if they are defined, otherwise scrollLeft and scrollTop. You can omit el to use a default value of window.

ES6

const getScrollPos = (el = window) =>
  ({x: (el.pageXOffset !== undefined) ? el.pageXOffset : el.scrollLeft,
    y: (el.pageYOffset !== undefined) ? el.pageYOffset : el.scrollTop});
// getScrollPos() -> {x: 0, y: 200}

ES5

var getScrollPos = function getScrollPos() {
  var el =
    arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : window;
  return {
    x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
    y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
  };
};
// getScrollPos() -> {x: 0, y: 200}

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Redirect to URL

Use window.location.href or window.location.replace() to redirect to url. Pass a second argument to simulate a link click (true - default) or an HTTP redirect (false).

ES6

const redirect = (url, asLink = true) =>
  asLink ? window.location.href = url : window.location.replace(url);
// redirect('https://google.com')

ES5

var redirect = function redirect(url) {
  var asLink =
    arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : true;
  return asLink ? (window.location.href = url) : window.location.replace(url);
};
// redirect('https://google.com')

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Scroll to top

Get distance from top using document.documentElement.scrollTop or document.body.scrollTop. Scroll by a fraction of the distance from top. Use window.requestAnimationFrame() to animate the scrolling.

ES6

const scrollToTop = _ => {
  const c = document.documentElement.scrollTop || document.body.scrollTop;
  if (c > 0) {
    window.requestAnimationFrame(scrollToTop);
    window.scrollTo(0, c - c / 8);
  }
};
// scrollToTop()

ES5

var scrollToTop = function scrollToTop(_) {
  var c = document.documentElement.scrollTop || document.body.scrollTop;
  if (c > 0) {
    window.requestAnimationFrame(scrollToTop);
    window.scrollTo(0, c - c / 8);
  }
};
// scrollToTop()

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Date

Get days difference between dates

Calculate the difference (in days) between to Date objects.

ES6

const getDaysDiffBetweenDates = (dateInitial, dateFinal) => (dateFinal - dateInitial) / (1000 * 3600 * 24);
// getDaysDiffBetweenDates(new Date("2017-12-13"), new Date("2017-12-22")) -> 9

ES5

var getDaysDiffBetweenDates = function getDaysDiffBetweenDates(
  dateInitial,
  dateFinal
) {
  return (dateFinal - dateInitial) / (1000 * 3600 * 24);
};
// getDaysDiffBetweenDates(new Date("2017-12-13"), new Date("2017-12-22")) -> 9

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Function

Chain asynchronous functions

Loop through an array of functions containing asynchronous events, calling next when each asynchronous event has completed.

ES6

const chainAsync = fns => { let curr = 0; const next = () => fns[curr++](next); next(); };
/*
chainAsync([
  next => { console.log('0 seconds'); setTimeout(next, 1000); },
  next => { console.log('1 second');  setTimeout(next, 1000); },
  next => { console.log('2 seconds'); }
])
*/

ES5

var chainAsync = function chainAsync(fns) {
  var curr = 0;
  var next = function next() {
    return fns[curr++](next);
  };
  next();
};
/*
chainAsync([
  next => { console.log('0 seconds'); setTimeout(next, 1000); },
  next => { console.log('1 second');  setTimeout(next, 1000); },
  next => { console.log('2 seconds'); }
])
*/

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Curry

Use recursion. If the number of provided arguments (args) is sufficient, call the passed function f. Otherwise return a curried function f that expects the rest of the arguments. If you want to curry a function that accepts a variable number of arguments (a variadic function, e.g. Math.min()), you can optionally pass the number of arguments to the second parameter arity.

ES6

const curry = (fn, arity = fn.length, ...args) =>
  arity <= args.length
    ? fn(...args)
    : curry.bind(null, fn, arity, ...args);
// curry(Math.pow)(2)(10) -> 1024
// curry(Math.min, 3)(10)(50)(2) -> 2

ES5

var curry = function curry(fn) {
  for (
    var _len = arguments.length,
      args = Array(_len > 2 ? _len - 2 : 0),
      _key = 2;
    _key < _len;
    _key++
  ) {
    args[_key - 2] = arguments[_key];
  }

  var arity =
    arguments.length > 1 && arguments[1] !== undefined
      ? arguments[1]
      : fn.length;
  return arity <= args.length
    ? fn.apply(undefined, args)
    : curry.bind.apply(curry, [null, fn, arity].concat(args));
};
// curry(Math.pow)(2)(10) -> 1024
// curry(Math.min, 3)(10)(50)(2) -> 2

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Pipe

Use Array.reduce() to pass value through functions.

ES6

const pipe = (...funcs) => arg => funcs.reduce((acc, func) => func(acc), arg);
// pipe(btoa, x => x.toUpperCase())("Test") -> "VGVZDA=="

ES5

var pipe = function pipe() {
  for (
    var _len = arguments.length, funcs = Array(_len), _key = 0;
    _key < _len;
    _key++
  ) {
    funcs[_key] = arguments[_key];
  }

  return function(arg) {
    return funcs.reduce(function(acc, func) {
      return func(acc);
    }, arg);
  };
};
// pipe(btoa, x => x.toUpperCase())("Test") -> "VGVZDA=="

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Promisify

Use currying to return a function returning a Promise that calls the original function. Use the ...rest operator to pass in all the parameters.

In Node 8+, you can use util.promisify

ES6

const promisify = func =>
  (...args) =>
    new Promise((resolve, reject) =>
      func(...args, (err, result) =>
        err ? reject(err) : resolve(result))
    );
// const delay = promisify((d, cb) => setTimeout(cb, d))
// delay(2000).then(() => console.log('Hi!')) -> Promise resolves after 2s

ES5

var promisify = function promisify(func) {
  return function() {
    for (
      var _len = arguments.length, args = Array(_len), _key = 0;
      _key < _len;
      _key++
    ) {
      args[_key] = arguments[_key];
    }

    return new Promise(function(resolve, reject) {
      return func.apply(
        undefined,
        args.concat([
          function(err, result) {
            return err ? <
10000
span class="pl-s1">reject(err) : resolve(result);
          }
        ])
      );
    });
  };
};
// const delay = promisify((d, cb) => setTimeout(cb, d))
// delay(2000).then(() => console.log('Hi!')) -> Promise resolves after 2s

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Run promises in series

Run an array of promises in series using Array.reduce() by creating a promise chain, where each promise returns the next promise when resolved.

ES6

const series = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());
// const delay = (d) => new Promise(r => setTimeout(r, d))
// series([() => delay(1000), () => delay(2000)]) -> executes each promise sequentially, taking a total of 3 seconds to complete

ES5

var series = function series(ps) {
  return ps.reduce(function(p, next) {
    return p.then(next);
  }, Promise.resolve());
};
// const delay = (d) => new Promise(r => setTimeout(r, d))
// series([() => delay(1000), () => delay(2000)]) -> executes each promise sequentially, taking a total of 3 seconds to complete

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Sleep

Delay executing part of an async function, by putting it to sleep, returning a Promise.

ES6

const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
/*
async function sleepyWork() {
  console.log('I\'m going to sleep for 1 second.');
  await sleep(1000);
  console.log('I woke up after 1 second.');
}
*/

ES5

var sleep = function sleep(ms) {
  return new Promise(function(resolve) {
    return setTimeout(resolve, ms);
  });
};
/*
async function sleepyWork() {
  console.log('I\'m going to sleep for 1 second.');
  await sleep(1000);
  console.log('I woke up after 1 second.');
}
*/

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Math

Collatz algorithm

If n is even, return n/2. Otherwise return 3n+1.

ES6

const collatz = n => (n % 2 == 0) ? (n / 2) : (3 * n + 1);
// collatz(8) --> 4
// collatz(5) --> 16

ES5

var collatz = function collatz(n) {
  return n % 2 == 0 ? n / 2 : 3 * n + 1;
};
// collatz(8) --> 4
// collatz(5) --> 16

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Distance between two points

Use Math.hypot() to calculate the Euclidean distance between two points.

ES6

const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);
// distance(1,1, 2,3) -> 2.23606797749979

ES5

var distance = function distance(x0, y0, x1, y1) {
  return Math.hypot(x1 - x0, y1 - y0);
};
// distance(1,1, 2,3) -> 2.23606797749979

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Divisible by number

Use the modulo operator (%) to check if the remainder is equal to 0.

ES6

const isDivisible = (dividend, divisor) => dividend % divisor === 0;
// isDivisible(6,3) -> true

ES5

var isDivisible = function isDivisible(dividend, divisor) {
  return dividend % divisor === 0;
};
// isDivisible(6,3) -> true

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Even or odd number

Checks whether a number is odd or even using the modulo (%) operator. Returns true if the number is even, false if the number is odd.

ES6

const isEven = num => num % 2 === 0;
// isEven(3) -> false

ES5

var isEven = function isEven(num) {
  return num % 2 === 0;
};
// isEven(3) -> false

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Factorial

Use recursion. If n is less than or equal to 1, return 1. Otherwise, return the product of n and the factorial of n - 1.

ES6

const factorial = n => n <= 1 ? 1 : n * factorial(n - 1);
// factorial(6) -> 720

ES5

var factorial = function factorial(n) {
  return n <= 1 ? 1 : n * factorial(n - 1);
};
// factorial(6) -> 720

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Fibonacci array generator

Create an empty array of the specific length, initializing the first two values (0 and 1). Use Array.reduce() to add values into the array, using the sum of the last two values, except for the first two.

ES6

const fibonacci = n =>
  Array(n).fill(0).reduce((acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i), []);
// fibonacci(5) -> [0,1,1,2,3]

ES5

var fibonacci = function fibonacci(n) {
  return Array(n)
    .fill(0)
    .reduce(function(acc, val, i) {
      return acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i);
    }, []);
};
// fibonacci(5) -> [0,1,1,2,3]

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Greatest common divisor (GCD)

Use recursion. Base case is when y equals 0. In this case, return x. Otherwise, return the GCD of y and the remainder of the division x/y.

ES6

const gcd = (x, y) => !y ? x : gcd(y, x % y);
// gcd (8, 36) -> 4

ES5

var gcd = function gcd(x, y) {
  return !y ? x : gcd(y, x % y);
};
// gcd (8, 36) -> 4

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Hamming distance

Use XOR operator (^) to find the bit difference between the two numbers, convert to binary string using toString(2). Count and return the number of 1s in the string, using match(/1/g).

ES6

const hammingDistance = (num1, num2) =>
  ((num1 ^ num2).toString(2).match(/1/g) || '').length;
// hammingDistance(2,3) -> 1

ES5

var hammingDistance = function hammingDistance(num1, num2) {
  return ((num1 ^ num2).toString(2).match(/1/g) || "").length;
};
// hammingDistance(2,3) -> 1

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Percentile

Use Array.reduce() to calculate how many numbers are below the value and how many are the same value and apply the percentile formula.

ES6

const percentile = (arr, val) => 
  100 * arr.reduce((acc,v) => acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0), 0) / arr.length;
// percentile([1,2,3,4,5,6,7,8,9,10], 6) -> 55

ES5

var percentile = function percentile(arr, val) {
  return (
    100 *
    arr.reduce(function(acc, v) {
      return acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0);
    }, 0) /
    arr.length
  );
};
// percentile([1,2,3,4,5,6,7,8,9,10], 6) -> 55

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Powerset

Use Array.reduce() combined with Array.map() to iterate over elements and combine into an array containing all combinations.

ES6

const powerset = arr =>
  arr.reduce((a, v) => a.concat(a.map(r => [v].concat(r))), [[]]);
// powerset([1,2]) -> [[], [1], [2], [2,1]]

ES5

var powerset = function powerset(arr) {
  return arr.reduce(
    function(a, v) {
      return a.concat(
        a.map(function(r) {
          return [v].concat(r);
        })
      );
    },
    [[]]
  );
};
// powerset([1,2]) -> [[], [1], [2], [2,1]]

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Round number to n digits

Use Math.round() and template literals to round the number to the specified number of digits. Omit the second argument, decimals to round to an integer.

ES6

const round = (n, decimals=0) => Number(`${Math.round(`${n}e${decimals}`)}e-${decimals}`);
// round(1.005, 2) -> 1.01

ES5

var round = function round(n) {
  var decimals =
    arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 0;
  return Number(Math.round(n + "e" + decimals) + "e-" + decimals);
};
// round(1.005, 2) -> 1.01

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Standard deviation

Use Array.reduce() to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then determine the standard deviation. You can omit the second argument to get the sample standard deviation or set it to true to get the population standard deviation.

ES6

const standardDeviation = (arr, usePopulation = false) => {
  const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
  return Math.sqrt(
    arr.reduce((acc, val) => acc.concat(Math.pow(val - mean, 2)), [])
       .reduce((acc, val) => acc + val, 0) / (arr.length - (usePopulation ? 0 : 1))
  );
};
// standardDeviation([10,2,38,23,38,23,21]) -> 13.284434142114991 (sample)
// standardDeviation([10,2,38,23,38,23,21], true) -> 12.29899614287479 (population)

ES5

var standardDeviation = function standardDeviation(arr) {
  var usePopulation =
    arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : false;

  var mean =
    arr.reduce(function(acc, val) {
      return acc + val;
    }, 0) / arr.length;
  return Math.sqrt(
    arr
      .reduce(function(acc, val) {
        return acc.concat(Math.pow(val - mean, 2));
      }, [])
      .reduce(function(acc, val) {
        return acc + val;
      }, 0) /
      (arr.length - (usePopulation ? 0 : 1))
  );
};
// standardDeviation([10,2,38,23,38,23,21]) -> 13.284434142114991 (sample)
// standardDeviation([10,2,38,23,38,23,21], true) -> 12.29899614287479 (population)

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Media

Speech synthesis (experimental)

Use SpeechSynthesisUtterance.voice and indow.speechSynthesis.getVoices() to convert a message to speech. Use window.speechSynthesis.speak() to play the message.

Learn more about the SpeechSynthesisUtterance interface of the Web Speech API.

ES6

const speak = message => {
  const msg = new SpeechSynthesisUtterance(message);
  msg.voice = window.speechSynthesis.getVoices()[0];
  window.speechSynthesis.speak(msg);
};
// speak('Hello, World') -> plays the message

ES5

var speak = function speak(message) {
  var msg = new SpeechSynthesisUtterance(message);
  msg.voice = window.speechSynthesis.getVoices()[0];
  window.speechSynthesis.speak(msg);
};
// speak('Hello, World') -> plays the message

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Object

Object from key-value pairs

Use Array.reduce() to create and combine key-value pairs.

ES6

const objectFromPairs = arr => arr.reduce((a, v) => (a[v[0]] = v[1], a), {});
// objectFromPairs([['a',1],['b',2]]) -> {a: 1, b: 2}

ES5

var objectFromPairs = function objectFromPairs(arr) {
  return arr.reduce(function(a, v) {
    return (a[v[0]] = v[1]), a;
  }, {});
};
// objectFromPairs([['a',1],['b',2]]) -> {a: 1, b: 2}

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Object to key-value pairs

Use Object.keys() and Array.map() to iterate over the object's keys and produce an array with key-value pairs.

ES6

const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]);
// objectToPairs({a: 1, b: 2}) -> [['a',1],['b',2]])

ES5

var objectToPairs = function objectToPairs(obj) {
  return Object.keys(obj).map(function(k) {
    return [k, obj[k]];
  });
};
// objectToPairs({a: 1, b: 2}) -> [['a',1],['b',2]])

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Shallow clone object

Use the object ...spread operator to spread the properties of the target object into the clone.

ES6

const shallowClone = obj => ({ ...obj });
/*
const a = { x: true, y: 1 };
const b = shallowClone(a);
a === b -> false
*/

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String

Anagrams of string (with duplicates)

Use recursion. For each letter in the given string, create all the partial anagrams for the rest of its letters. Use Array.map() to combine the letter with each partial anagram, then Array.reduce() to combine all anagrams in one array. Base cases are for string length equal to 2 or 1.

ES6

const anagrams = str => {
  if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
  return str.split('').reduce((acc, letter, i) =>
    acc.concat(anagrams(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)), []);
};
// anagrams('abc') -> ['abc','acb','bac','bca','cab','cba']

ES5

var anagrams = function anagrams(str) {
  if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
  return str.split("").reduce(function(acc, letter, i) {
    return acc.concat(
      anagrams(str.slice(0, i) + str.slice(i + 1)).map(function(val) {
        return letter + val;
      })
    );
  }, []);
};
// anagrams('abc') -> ['abc','acb','bac','bca','cab','cba']

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Capitalize first letter of every word

Use replace() to match the first character of each word and toUpperCase() to capitalize it.

ES6

const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
// capitalizeEveryWord('hello world!') -> 'Hello World!'

ES5

var capitalizeEveryWord = function capitalizeEveryWord(str) {
  return str.replace(/\b[a-z]/g, function(char) {
    return char.toUpperCase();
  });
};
// capitalizeEveryWord('hello world!') -> 'Hello World!'

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Capitalize first letter

Use slice(0,1) and toUpperCase() to capitalize first letter, slice(1) to get the rest of the string. Omit the lowerRest parameter to keep the rest of the string intact, or set it to true to convert to lower case.

ES6

const capitalize = (str, lowerRest = false) =>
  str.slice(0, 1).toUpperCase() + (lowerRest ? str.slice(1).toLowerCase() : str.slice(1));
// capitalize('myName', true) -> 'Myname'

ES5

var capitalize = function capitalize(str) {
  var lowerRest =
    arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : false;
  return (
    str.slice(0, 1).toUpperCase() +
    (lowerRest ? str.slice(1).toLowerCase() : str.slice(1))
  );
};
// capitalize('myName', true) -> 'Myname'

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Check for palindrome

Convert string toLowerCase() and use replace() to remove non-alphanumeric characters from it. Then, split('') into individual characters, reverse(), join('') and compare to the original, unreversed string, after converting it tolowerCase().

ES6

const palindrome = str => {
  const s = str.toLowerCase().replace(/[\W_]/g,'');
  return s === s.split('').reverse().join('');
}
// palindrome('taco cat') -> true

ES5

var palindrome = function palindrome(str) {
  var s = str.toLowerCase().replace(/[\W_]/g, "");
  return (
    s ===
    s
      .split("")
      .reverse()
      .join("")
  );
};
// palindrome('taco cat') -> true

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Reverse a string

Use array destructuring and Array.reverse() to reverse the order of the characters in the string. Combine characters to get a string using join('').

ES6

const reverseString = str => [...str].reverse().join('');
// reverseString('foobar') -> 'raboof'

ES5

function _toConsumableArray(arr) {
  if (Array.isArray(arr)) {
    for (var i = 0, arr2 = Array(arr.length); i < arr.length; i++) {
      arr2[i] = arr[i];
    }
    return arr2;
  } else {
    return Array.from(arr);
  }
}

var reverseString = function reverseString(str) {
  return []
    .concat(_toConsumableArray(str))
    .reverse()
    .join("");
};
// reverseString('foobar') -> 'raboof'

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Sort characters in string (alphabetical)

Split the string using split(''), Array.sort() utilizing localeCompare(), recombine using join('').

ES6

const sortCharactersInString = str =>
  str.split('').sort((a, b) => a.localeCompare(b)).join('');
// sortCharactersInString('cabbage') -> 'aabbceg'

ES5

var sortCharactersInString = function sortCharactersInString(str) {
  return str
    .split("")
    .sort(function(a, b) {
      return a.localeCompare(b);
    })
    .join("");
};
// sortCharactersInString('cabbage') -> 'aabbceg'

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Truncate a String

Determine if the string's length is greater than num. Return the string truncated to the desired length, with ... appended to the end or the original string.

ES6

const truncate = (str, num) =>
  str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;
// truncate('boomerang', 7) -> 'boom...'

ES5

var truncate = function truncate(str, num) {
  return str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + "..." : str;
};
// truncate('boomerang', 7) -> 'boom...'

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Utility

Escape regular expression

Use replace() to escape special characters.

ES6

const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
// escapeRegExp('(test)') -> \\(test\\)

ES5

var escapeRegExp = function escapeRegExp(str) {
  return str.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
};
// escapeRegExp('(test)') -> \\(test\\)

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Get native type of value

Returns lower-cased constructor name of value, "undefined" or "null" if value is undefined or null

ES6

const getType = v =>
  v === undefined ? 'undefined' : v === null ? 'null' : v.constructor.name.toLowerCase();
// getType(new Set([1,2,3])) -> "set"

ES5

var getType = function getType(v) {
  return v === undefined
    ? "undefined"
    : v === null ? "null" : v.constructor.name.toLowerCase();
};
// getType(new Set([1,2,3])) -> "set"

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Is array

Use Array.isArray() to check if a value is classified as an array.

ES6

const isArray = val => !!val && Array.isArray(val);
// isArray(null) -> false
// isArray([1]) -> true

ES5

var isArray = function isArray(val) {
  return !!val && Array.isArray(val);
};
// isArray(null) -> false
// isArray([1]) -> true

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Is boolean

Use typeof to check if a value is classified as a boolean primitive.

ES6

const isBoolean = val => typeof val === 'boolean';
// isBoolean(null) -> false
// isBoolean(false) -> true

ES5

var isBoolean = function isBoolean(val) {
  return typeof val === "boolean";
};
// isBoolean(null) -> false
// isBoolean(false) -> true

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Is function

Use typeof to check if a value is classified as a function primitive.

ES6

const isFunction = val => val && typeof val === 'function';
// isFunction('x') -> false
// isFunction(x => x) -> true

ES5

var isFunction = function isFunction(val) {
  return val && typeof val === "function";
};
// isFunction('x') -> false
// isFunction(x => x) -> true

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Is number

Use typeof to check if a value is classified as a number primitive.

ES6

const isNumber = val => typeof val === 'number';
// isNumber('1') -> false
// isNumber(1) -> true

ES5

var isNumber = function isNumber(val) {
  return typeof val === "number";
};
// isNumber('1') -> false
// isNumber(1) -> true

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Is string

Use typeof to check if a value is classified as a string primitive.

ES6

const isString = val => typeof val === 'string';
// isString(10) -> false
// isString('10') -> true

ES5

var isString = function isString(val) {
  return typeof val === "string";
};
// isString(10) -> false
// isString('10') -> true

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Is symbol

Use typeof to check if a value is classified as a symbol primitive.

ES6

const isSymbol = val => typeof val === 'symbol';
// isSymbol('x') -> false
// isSymbol(Symbol('x')) -> true

ES5

var _typeof =
  typeof Symbol === "function" && typeof Symbol.iterator === "symbol"
    ? function(obj) {
        return typeof obj;
      }
    : function(obj) {
        return obj &&
        typeof Symbol === "function" &&
        obj.constructor === Symbol &&
        obj !== Symbol.prototype
          ? "symbol"
          : typeof obj;
      };

var isSymbol = function isSymbol(val) {
  return (typeof val === "undefined" ? "undefined" : _typeof(val)) === "symbol";
};
// isSymbol('x') -> false
// isSymbol(Symbol('x')) -> true

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Measure time taken by function

Use console.time() and console.timeEnd() to measure the difference between the start and end times to determine how long the callback took to execute.

ES6

const timeTaken = callback => {
  console.time('timeTaken');
  const r = callback();
  console.timeEnd('timeTaken');
  return r;
};
// timeTaken(() => Math.pow(2, 10)) -> 1024
// (logged): timeTaken: 0.02099609375ms

ES5

var timeTaken = function timeTaken(callback) {
  console.time("timeTaken");
  var r = callback();
  console.timeEnd("timeTaken");
  return r;
};
// timeTaken(() => Math.pow(2, 10)) -> 1024
// (logged): timeTaken: 0.02099609375ms

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Number to array of digits

Convert the number to a string, use split() to convert build an array. Use Array.map() and parseInt() to transform each value to an integer.

ES6

const digitize = n => (''+n).split('').map(i => parseInt(i));
// digitize(2334) -> [2, 3, 3, 4]

ES5

var digitize = function digitize(n) {
  return ("" + n).split("").map(function(i) {
    return parseInt(i);
  });
};
// digitize(2334) -> [2, 3, 3, 4]

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Ordinal suffix of number

Use the modulo operator (%) to find values of single and tens digits. Find which ordinal pattern digits match. If digit is found in teens pattern, use teens ordinal.

ES6

const toOrdinalSuffix = num => {
  const int = parseInt(num), digits = [(int % 10), (int % 100)],
    ordinals = ['st', 'nd', 'rd', 'th'], oPattern = [1, 2, 3, 4],
    tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
  return oPattern.includes(digits[0]) && !tPattern.includes(digits[1]) ? int + ordinals[digits[0] - 1] : int + ordinals[3];
};
// toOrdinalSuffix("123") -> "123rd"

ES5

var toOrdinalSuffix = function toOrdinalSuffix(num) {
  var int = parseInt(num),
    digits = [int % 10, int % 100],
    ordinals = ["st", "nd", "rd", "th"],
    oPattern = [1, 2, 3, 4],
    tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
  return oPattern.includes(digits[0]) && !tPattern.includes(digits[1])
    ? int + ordinals[digits[0] - 1]
    : int + ordinals[3];
};
// toOrdinalSuffix("123") -> "123rd"

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Random integer in range

Use Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.

ES6

const randomIntegerInRange = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;
// randomIntegerInRange(0, 5) -> 2

ES5

var randomIntegerInRange = function randomIntegerInRange(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
};
// randomIntegerInRange(0, 5) -> 2

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Random number in range

Use Math.random() to generate a random value, map it to the desired range using multiplication.

ES6

const randomInRange = (min, max) => Math.random() * (max - min) + min;
// randomInRange(2,10) -> 6.0211363285087005

ES5

var randomInRange = function randomInRange(min, max) {
  return Math.random() * (max - min) + min;
};
// randomInRange(2,10) -> 6.0211363285087005

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RGB to hexadecimal

Convert given RGB parameters to hexadecimal string using bitwise left-shift operator (<<) and toString(16), then padStart(6,'0') to get a 6-digit hexadecimal value.

ES6

const rgbToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0');
// rgbToHex(255, 165, 1) -> 'ffa501'

ES5

var rgbToHex = function rgbToHex(r, g, b) {
  return ((r << 16) + (g << 8) + b).toString(16).padStart(6, "0");
};
// rgbToHex(255, 165, 1) -> 'ffa501'

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Swap values of two variables

Use array destructuring to swap values between two variables.

ES6

[varA, varB] = [varB, varA];
// [x, y] = [y, x]

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URL parameters

Use match() with an appropriate regular expression to get all key-value pairs, Array.reduce() to map and combine them into a single object. Pass location.search as the argument to apply to the current url.

ES6

const getUrlParameters = url =>
  url.match(/([^?=&]+)(=([^&]*))/g).reduce(
    (a, v) => (a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1), a), {}
  );
// getUrlParameters('http://url.com/page?name=Adam&surname=Smith') -> {name: 'Adam', surname: 'Smith'}

ES5

var getUrlParameters = function getUrlParameters(url) {
  return url.match(/([^?=&]+)(=([^&]*))/g).reduce(function(a, v) {
    return (a[v.slice(0, v.indexOf("="))] = v.slice(v.indexOf("=") + 1)), a;
  }, {});
};
// getUrlParameters('http://url.com/page?name=Adam&surname=Smith') -> {name: 'Adam', surname: 'Smith'}

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UUID generator

Use crypto API to generate a UUID, compliant with RFC4122 version 4.

ES6

const uuid = _ =>
  ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
    (c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
  );
// uuid() -> '7982fcfe-5721-4632-bede-6000885be57d'

ES5

var uuid = function uuid(_) {
  return ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, function(c) {
    return (c ^
      (crypto.getRandomValues(new Uint8Array(1))[0] &
        (15 >> (c / 4)))).toString(16);
  });
};
// uuid() -> '7982fcfe-5721-4632-bede-6000885be57d'

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Validate email

Use a regular experssion to check if the email is valid. Returns true if email is valid, false if not.

ES6

const validateEmail = str =>
  /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/.test(str);
// validateEmail(mymail@gmail.com) -> true

ES5

var validateEmail = function validateEmail(str) {
  return /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/.test(
    str
  );
};
// validateEmail(mymail@gmail.com) -> true

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Validate number

Use !isNaN in combination with parseFloat() to check if the argument is a number. Use isFinite() to check if the number is finite. Use Number() to check if the coercion holds.

ES6

const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;
// validateNumber('10') -> true

ES5

var validateNumber = function validateNumber(n) {
  return !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;
};
// validateNumber('10') -> true

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Value or default

Returns value, or default value if passed value is falsy.

ES6

const valueOrDefault = (value, d) => value || d;
// valueOrDefault(NaN, 30) -> 30

ES5

var valueOrDefault = function valueOrDefault(value, d) {
  return value || d;
};
// valueOrDefault(NaN, 30) -> 30

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Name		Name	Last commit message	Last commit date
Latest commit History 16 Commits
images		images
scripts		scripts
snippets		snippets
static-parts		static-parts
.gitignore		.gitignore
CONTRIBUTING.md		CONTRIBUTING.md
LICENSE		LICENSE
README.md		README.md
package.json		package.json
snippet-template.md		snippet-template.md
tag_database		tag_database
yarn.lock		yarn.lock

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cdscawd/seconds-of-code

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seconds of code

Table of Contents

Array

Browser

Date

Function

Math

Media

Object

String

Utility

Array

Array concatenation

拼接

Array difference

差异

Array intersection

交叉

Array union

联合

Average of array of numbers

平均

Chunk array

重组整列

Compact

有效值

Count occurrences of a value in array

存在总数

Deep flatten array

深平阵数组

Drop elements in array

提取条件项

Fill array

Filter out non-unique values in an array

Flatten array up to depth

Flatten array

Get max value from array

Get min value from array

Group by

Head of list

Initial of list

Initialize array with range

Initialize array with values

Last of list

Median of array of numbers

Nth element of array

Pick

Shuffle array

Similarity between arrays

Sum of array of numbers

Tail of list

Take

Unique values of array

Browser

Bottom visible

Current URL

Element is visible in viewport

Get scroll position

Redirect to URL

Scroll to top

Date

Get days difference between dates

Function

Chain asynchronous functions

Curry

Pipe

Promisify

Run promises in series

Sleep

Math

Collatz algorithm

Distance between two points

Divisible by number

Even or odd number

Packages