javascript - 如何确定变量是“未定义”还是“空”？(How to determine if variable is 'undefined' or 'null'?)

Question

How do I determine if variable is undefined or null ?

(如何确定变量是否undefined或为null ？)

My code is as follows:

(我的代码如下：)

var EmpName = $("div#esd-names div#name").attr('class');
if(EmpName == 'undefined'){
  //DO SOMETHING
};

<div id="esd-names">
  <div id="name"></div>
</div>

But if I do this, the JavaScript interpreter halts execution.

(但是，如果执行此操作，JavaScript解释器将停止执行。)

  ask by sadmicrowave translate from so

Answer 1

You can use the qualities of the abstract equality operator to do this:

(您可以使用抽象相等运算符的品质来做到这一点：)

if (variable == null){
    // your code here.
}

Because null == undefined is true, the above code will catch both null and undefined .

(因为null == undefined为true，所以上面的代码将捕获null和undefined 。)