Check if variable is 'undefined' or 'null'

to check if javascript variable is undefined or nul use :

      if(typeof variable_here === 'undefined'){
         // your code here.
      };

      if(typeof variable_here === 'undefined'){
         // your code here.
      };

1. <code>
2. if(typeof variable_here === 'undefined'){
3. // your code here.
4. };
6. </code>

<code>
      if(typeof variable_here === 'undefined'){
         // your code here.
      };

</code>

OR :

     if(! variable_here){
        // your code here.
     };

     if(! variable_here){
        // your code here.
     };

1. <code>
2. if(! variable_here){
3. // your code here.
4. };
6. </code>

<code>
     if(! variable_here){
        // your code here.
     };

</code>