Check if a check box is checked or not (js/jquery)

I want to check if a certain check box is selected using JavaScript/jQuery.

Here is the code I tried:

var a;
     if ($("#add_desc").checked == 1){
         a = "true";
     }else{
         a= "false";
     }
 

I have also tried:

var a;
     if ($("#add_desc").checked){
         a= "true";
     }else{
         a= "false";
     }
 

It always returns false once I alert the variable a.

Any idea why it won't work for me? Am I doing it wrong?

Thanks!

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