jQuery .trigger("change") not working

Question

I can't get .trigger("change") to work. Anyone know why?

jQuery(document).ready(function () {

    jQuery("select[id='DROPDOWNID']").change(function () {

        var selectedIndex = jQuery("select[id='DROPDOWNID']").prop('selectedIndex');

        switch (selectedIndex) {
            case 0:
                hideVarforProspekt();
                break;
            case 1:
                hideOrdervarde();
                break;
            case 2:

                break;
            case 3:
                hideSektor();
                break;
        }
    });

    ** jQuery("select[id='DROPDOWNID']").trigger("change"); **


    function hideVarforProspekt() {
        jQuery("input[id='IDFROMSHAREPOINT']").closest('tr').hide();
    }

    function hideSektor() {
        jQuery("table[id='IDFROMSHAREPOINT']").closest('tr').hide();
    }

    function hideUppskOrder() {
        jQuery("input[id='IDFROMSHAREPOINT']").closest('tr').hide();
    }
});

Answer 1

Change event handler should be defined before calling the .trigger('change') or .change()

Below are 2 scenarios.

Scenario 1: where change event is called before it is defined.

    $(document).ready(function() 
    {
       $('#selector').change();   or  $('#selector').trigger('change');
       $('#selector').on('change', function(){

        });
    });

Scenario 2: where change event handler is defined before calling it

$(document).ready(function() 
{
    $('#selector').on('change', function(){

    });
    $('#selector').change();   or  $('#selector').trigger('change');
});

For me issue was fixed when I use scenario2. Hope this helps!!

Answer 2

Sometimes the usage of trigger is not necessary:

// use just jQuery("#DROPDOWNID") instead
var select = jQuery("select[id='DROPDOWNID']");

// placing the handler in separate function
var changeHandler = function () {
    var selectedIndex = select.prop('selectedIndex');
    switch(selectedIndex) {
        case 0:
            hideVarforProspekt();
        break;
        case 1:
            hideOrdervarde();
        break;
        case 2:

        break;
        case 3:
            hideSektor();
        break;
    }
}

// cache your jQuery selectors. It's a good practice
// and improves the readability
select.change(changeHandler);

// triggering
changeHandler();