为什么javascript将0视为空字符串? [英] Why javascript treats 0 equal to empty string?

问题描述

可能的重复:
隐含字符串比较，0=''，但 1='1'

在javascript中执行以下情况，我得到0等于''(空字符串)

Executing the following case in javascript, I get 0 equal to '' (an empty string)

var a   =   0;
var b   =   '';//empty string
if(a==b){
    console.log('equal');//this is printed in console
}else{
    console.log('not equal');
}

谁能指导一下这背后的原因是什么?

Could anyone guide that what is the reason behind this?

推荐答案

引用文档 (MDN):

等于 (==)

如果两个操作数的类型不同，JavaScript 会转换操作数然后应用严格的比较.如果任一操作数是数字或布尔值，如果可能，将操作数转换为数字；别的如果任一操作数是字符串，则另一个操作数将转换为如果可能，字符串.

If the two operands are not of the same type, JavaScript converts the operands then applies strict comparison. If either operand is a number or a boolean, the operands are converted to numbers if possible; else if either operand is a string, the other operand is converted to a string if possible.

因为这里的a操作数类型是Number，b也被转换为Number.并且 Number('') 计算结果为 0.

As a operand type here is Number, b gets converted to Number as well. And Number('') evaluates to 0.

有时这可能会令人惊讶.考虑一下，例如:

This can be quite surprising sometimes. Consider this, for example:

console.log(0 == '0');  // true
console.log(0 == '');   // true
console.log('' == '0'); // O'RLY?

... 或者这个:

console.log(false == undefined); // false
console.log(false == null);      // false
console.log(null == undefined);  // fal.... NO WAIT!

...这正是为什么几乎总是建议使用 ===(严格相等)运算符的原因.

...and that's exactly why it's almost always recommended to use === (strict equality) operator instead.

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