<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>
<body>
<script>
//补充NaN和谁都不相等
var a
// a为何值时条件成立
if(a == 1 && a == 2 && a == 3){
console.log(1)
}
//答案
a = {
n:0,
toString:function(){
return this.n+=1
}
}
//对象数据类型会调用toString方法再比较
</script>
</body>
</html>