For loop in jquery . I need to run scripts for 20 time each with with increment
<p>I have no idea about loop in jquery. I want the following code to be run as for loop from product1 to product20 and check the same if quantity1 to quantity20 have no value then set it to 1.</p>

<pre><code>$('#product1').change(function() {
    if(  $('#quantity1').val().length == 0 ){
        $('#quantity1').val("1");
    }
});

$('#product2').change(function() {
    if(  $('#quantity2').val().length == 0 ){
        $('#quantity2').val("1");
    }
});
</code></pre>

<p>Thank you in advance.</p>
