html – Why does the jquery change event not trigger when I set the value of a select using val()?

The Question :

381 people think this question is useful

The logic in the change() event handler is not being run when the value is set by val(), but it does run when user selects a value with their mouse. Why is this?

<select id="single">
    <option>Single</option>
    <option>Single2</option>
</select>

<script>
    $(function() {
        $(":input#single").change(function() {
           /* Logic here does not execute when val() is used */
        });
    });

    $("#single").val("Single2");
</script>

The Question Comments :

The Answer 1

595 people think this answer is useful

Because the change event requires an actual browser event initiated by the user instead of via javascript code.

Do this instead:

$("#single").val("Single2").trigger('change');

or

$("#single").val("Single2").change();

The Answer 2

45 people think this answer is useful

I believe you can manually trigger the change event with trigger():

$("#single").val("Single2").trigger('change');

Though why it doesn’t fire automatically, I have no idea.

The Answer 3

10 people think this answer is useful

Adding this piece of code after the val() seems to work:

$(":input#single").trigger('change');

The Answer 4

8 people think this answer is useful

As far as I can read in API’s. The event is only fired when the user clicks on an option.

http://api.jquery.com/change/

For select boxes, checkboxes, and radio buttons, the event is fired immediately when the user makes a selection with the mouse, but for the other element types the event is deferred until the element loses focus.

The Answer 5

6 people think this answer is useful

To make it easier add a custom function and call it when ever you want that changing the value also trigger change

$.fn.valAndTrigger = function (element) {
    return $(this).val(element).trigger('change');
}

and

$("#sample").valAndTirgger("NewValue");

Or you can override the val function to always call the change when the val is called

(function ($) {
    var originalVal = $.fn.val;
    $.fn.val = function (value) {
        this.trigger("change");
        return originalVal.call(this, value);
    };
})(jQuery);

Sample at http://jsfiddle.net/r60bfkub/

The Answer 6

3 people think this answer is useful

In case you don’t want to mix up with default change event you can provide your custom event

$('input.test').on('value_changed', function(e){
    console.log('value changed to '+$(this).val());
});

to trigger the event on value set, you can do

$('input.test').val('I am a new value').trigger('value_changed');

The Answer 7

3 people think this answer is useful

I ran into the same issue while using CMB2 with WordPress and wanted to hook into the change event of a file upload metabox.

So in case you’re not able to modify the code that invokes the change (in this case the CMB2 script), use the code below. The trigger is being invoked AFTER the value is set, otherwise your change eventHandler will work, but the value will be the previous one, not the one being set.

Here’s the code i use:

(function ($) {
    var originalVal = $.fn.val;
    $.fn.val = function (value) {
        if (arguments.length >= 1) {
            // setter invoked, do processing
            return originalVal.call(this, value).trigger('change');
        }
        //getter invoked do processing
        return originalVal.call(this);
    };
})(jQuery);

The Answer 8

2 people think this answer is useful

If you’ve just added the select option to a form and you wish to trigger the change event, I’ve found a setTimeout is required otherwise jQuery doesn’t pick up the newly added select box:

window.setTimeout(function() { jQuery('.languagedisplay').change();}, 1);

The Answer 9

1 people think this answer is useful
$(":input#single").trigger('change');

This worked for my script. I have 3 combos & bind with chainSelect event, I need to pass 3 values by url & default select all drop down. I used this

$('#machineMake').val('<?php echo $_GET['headMake']; ?>').trigger('change');

And the first event worked.

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