Javascript while loop freezing page

Question

So the page keeps freezing when i run this function on firefox and google chrome i tried using a for loop didn't work as expected any ideas?

Thanks

   function grab_users() {

    var start_id = document.getElementById('start_range');
    start_id = start_id.value;

    var end_id = document.getElementById('end_range');
    end_id = end_id.value;

    var grabbed = document.getElementById('grabbed_users');
    while (start_id < end_id) {
        $.ajax({
            url: "php/extract.php",
            type: 'GET',
            data: {'start_range': start_id},
            success: function(res) {
                var usernames = res;

                if (!usernames.valueOf() == "") {
                    usernames = usernames.replace('</br>', '');
                    grabbed.value += usernames + '\n';
                }
            }
        });
        start_id+=1;
    }
}

The page should indeed 'freeze' until it completes. How many iterations are we talking about? — Luan Nico
– Luan Nico, Commented Jan 31, 2015 at 9:35
Looks like the usual AJAX problem, updating grabbed from inside the callback... — elclanrs
– elclanrs, Commented Jan 31, 2015 at 9:38
@elclanrs: The OP's not using anything inside the success handler that varies for the loop, so that part's okay. (Doing a huge number of overlapping ajax calls, on the other hand...) — T.J. Crowder
– T.J. Crowder, Commented Jan 31, 2015 at 9:48
note that start_id is a string, and adding 1 doesn't do what the OP thinks — adeneo
– adeneo, Commented Jan 31, 2015 at 9:49

Dr.Molle · Accepted Answer · 2015-01-31 09:55:22Z

2

the values of inputs are always strings, you must convert them to Numbers before you use them, otherwise both, the comparision and the incrementation of start_id will not give the expected results(what ends in a infinite loop):

var start_id = parseInt(document.getElementById('start_range').value,10);
var end_id = parseInt(document.getElementById('end_range').value,10);

Suppose your start_id is "20" and your end_id is "30". You'll start out with "20" < "30", which is true; then on the next loop, you'll append 1 to the start_id string, giving us "201" < "30". That's a string comparison, and so it's also true. Then "2011" < "30", which is also true. And so on.

Using numbers corrects this.

edited Jan 31, 2015 at 9:55

answered Jan 31, 2015 at 9:50

Dr.Molle

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