javascript - Different "return null" results in Chrome and Firefox -

given following code:

jquery(document).ready(function($) {        $('[name="clickabletd"]').click(function() {              window.document.location = $(this).attr("href");        });  });      function add(id) {      	      var stock = "2";  	      var quantity = prompt("select quantity:", 1);          if (quantity == null) {          return null;      }          else if (quantity <= stock) {          alert("good");      }  	  	else if (quantity > stock) {          alert("over");  	}  	  	else if (isnan(quantity)) {          alert("nan");      }  }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>      <table border="1">    <tr>      <td name="clickabletd" href="javascript:add('1')">        <a>click</a>      </td>    </tr>  </table>

if user returns null value (by clicking cancel) using chrome browser nothing happens expected.

but if user using firefox redirected url add() , display null text string on screen.

why firefox react differently chrome?

i've been having trouble finding detailed specification of how javascript: urls work, , they're supposed when code returns other string or undefined. looks chrome , firefox have taken different approaches in case. chrome treats them undefined, , doesn't change page contents. ff various things: if returns null displays string null; if returns object single property, displays value of property.

use return void(0) or return undefined instead of null better compatibility between browsers.