js当中==和===的区别，!=和!==的区别

==和===的对比，先看下==

<script type="text/javascript">        window.onload= function(){            var a = 2;            if(a == 2) {                console.info("2");            }            if(a == "2") {                console.info("a");            }        }    </script>

这里的输出是

2a

可见在比较时只要是值相等就可以，自动进行类型转换。再看看===

<script type="text/javascript">        window.onload= function(){            var a = 2;            if(a === 2) {                console.info("2");            }            if(a === "2") {                console.info("a");            }        }    </script>

===的输出只有

2

可见===在比较是值和类型都相同才为true
接下来看看！=和！==

<script type="text/javascript">        window.onload= function(){            var a = 3;            var b = "3";            console.info(a != b);        }    </script>

上面输出为false，自动进行了类型转换

<script type="text/javascript">        window.onload= function(){            var a = 3;            var b = "3";            console.info(a !== b);        }    </script>

上面的输出为true