如何确定变量是否为"未定义"或"空"？

Question

How do I determine if variable is undefined or null? My code is as follows:

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.

转载于:https://stackoverflow.com/questions/2647867/how-to-determine-if-variable-is-undefined-or-null

Answer 1

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

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

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