JavaScript中==和===区别

在我们的日常编码中对于===是不常用的，但是它很重要

===：表示绝对相等（严格）

!==:表示不绝对相等

==：表示相等（不严格）

!=：表示不相等

看一下列子：

null==undefined  结果是为true

null===undefined 结果是为false

0==false，0=='',''==false 结果都是为true

0===false，0==='',''===false 结果都是为false

反之：!=和!==结果和上面相反

测试代码：

alert("null==0 is "+(null==0)+" "+"null==undefined is "+(null==undefined)+" "+"null=='' is "+(''==null)+" "+"null==false is "+(null==false)+" "+"0=='' is "+(0=='')+" "+"0==false is "+(0==false)+" "+"0==undefined is "+(0==undefined)+" "+"''==false is "+(''==false)+" "+"''==undefined is "+(''==undefined)+" "+"false==undefined is "+(false==undefined));

alert("null===0 is "+(null===0)+" "+"null===undefined is "+(null===undefined)+" "+"null==='' is "+(''===null)+" "+"null===false is "+(null===false)+" "+"0==='' is "+(0==='')+" "+"0===false is "+(0===false)+" "+"0===undefined is "+(0===undefined)+" "+"''===false is "+(''===false)+" "+"''===undefined is "+(''===undefined)+" "+"false===undefined is "+(false===undefined));