How to determine if jquery is empty

Jquery method to determine whether it is empty: 1. Method one [if(C==null||C==undefined||C=="")]; 2. Method two [if(C. length==0)]; 3. Method three [if (C) {//code}].

Jquery method to determine whether it is empty:

It needs to be used when writing verification when the input empty value is not When it is empty, perform verification, the code is as follows

if($("#email").val()) {
          var isEmail = /^([\.a-zA-Z0-9_-])+@([a-zA-Z0-9_-])+(\.[a-zA-Z0-9_-])+/;  
           if(!isEmail.test($("#email").val())){
              $('#popContent').text('请您输入正确的邮箱');
             $('#popMask').modal('open');
            return false;
           }
 }

I also take the opportunity to summarize the jquery method of judging whether it is empty

var C = $("类名或者id").val();

(1)

if(C==null||C==undefined||C==""){
//代码
}

(2)

if(C.length==0){
//代码
}

(3)

if(C){
//代码
}

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