妙用Javascript运算符“||”和“&&” #3

Wscats · 2016-04-15T07:53:47Z

var a = 1;
        var b = 2;
        if (a < b && a == 1) {
            //console.log("&&");
        }
        //上面改写
        a < b && a == 1 && console.log("&&");
        if (a > b || a == 1) {
            //console.log("||");
        }
        //
        a > b || a == 1 && console.log("||");
        //&&前面为真运行后面 否则不运行
        var c = (a == 1) && 3
        var d = (a == 2) && 3
        console.log(c); //3     取了后面的3
        console.log(d); //false 取了前面的false
        //||前面为假运行后面 否则不运行
        var c = (a == 1) || 3
        var d = (a == 2) || 3
        console.log(c); //true
        console.log(d); //3
        //巧用
        var e = 0;
        var f;
        switch (f) {
            case 5:
                e = 1;
                break;
            case 10:
                e = 2;
                break;
            case 12:
                e = 3;
                break;
            case 15:
                e = 4;
                break;
            default:
                e = 0;
                break;
        }
        var e = (f == 5 && 1) || (f == 10 && 2) || (f == 12 && 3) || (f == 15 && 4) || 0;
        console.log(e); //0

总结理解为
&&遇上假就停止，并返回这个假，相反遇到真就继续执行直到拿最后一个
||遇上真就停止，并返回这个真，相反遇到假就继续执行直到拿最后一个
这样会不会好理解多
注意：非0的整数都为true，undefined、null和空字符串”" 为false。

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Wscats closed this as completed Aug 22, 2019

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妙用Javascript运算符“||”和“&&” #3

妙用Javascript运算符“||”和“&&” #3

妙用Javascript运算符“||”和“&&” #3

妙用Javascript运算符“||”和“&&” #3

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