jQueryJavascript: setInterval check if DOM element exists? - Stack Overflow

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var check; function showLoader() { $('#mc_signup_form').prepend(' loading …'); check_init(); }

    function check_init() {
        check = setInterval('check_trigger()', 300);
    }

    function check_clear() {
        clearInterval(check);
    }

    function check_trigger() {
        if ( $('.mc_error_msg').length == 0 || $('.mc_success_msg').length == 0 ) {
            $('#mc_signup_form .loading').remove();
            check_clear();
        }
    }

i wonder why my browser keeps telling me that check_trigger() doesn't exist? I'm initiating a setInterval inside of my showLoader() function. It should trigger check_trigger. When one of the two divs (.mc_error_msg or .mc_success_msg) exists i want to clear the Interval.

What am I doing wrong?

var check; function showLoader() { $('#mc_signup_form').prepend(' loading …'); check_init(); }

    function check_init() {
        check = setInterval('check_trigger()', 300);
    }

    function check_clear() {
        clearInterval(check);
    }

    function check_trigger() {
        if ( $('.mc_error_msg').length == 0 || $('.mc_success_msg').length == 0 ) {
            $('#mc_signup_form .loading').remove();
            check_clear();
        }
    }

i wonder why my browser keeps telling me that check_trigger() doesn't exist? I'm initiating a setInterval inside of my showLoader() function. It should trigger check_trigger. When one of the two divs (.mc_error_msg or .mc_success_msg) exists i want to clear the Interval.

What am I doing wrong?

• javascript
• jquery
• setinterval

Share Improve this question Follow asked Aug 4, 2010 at 5:39 mattmatt 44.4k107107 gold badges268268 silver badges402402 bronze badges 2

• have you try to put check_trigger() above check_init()? – airmanx86 Commented Aug 4, 2010 at 5:41
• @mathiregister, what's the scope of the code? because setInterval() would be running under "window" / global object, it might not find check_trigger(). – airmanx86 Commented Aug 4, 2010 at 5:50

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5 Answers 5

Sorted by: Reset to default 1

it should be check_trigger only remove outside the single or double quote...

also use setTimeout instead of setInterval so you can get rid of the global variable

Avoid double evaluation

By putting that function into quotes, ECMA-/Javascript will eval that code, which is just unbelievable slow'ish. So always use a function reference withing setTimeout / setInterval:

setInterval(function(){
    check_trigger();
}, 300);

or directly

setInterval(check_trigger, 300);

If you remove the elements in question by yourself somewhere, it might be an interesting approach to hook the jQuery .remove() or .detach() method (If you call those to remove the element).

That could look like:

var hookRemove = $.fn.remove;

$.fn.remove    = function(){
    if(this.id === 'something'){
       // hoorray! we found it
    }

    hookRemove.apply(this, arguments);
};

Remember your're dealing with an jQuery object within the hook. So actually this could also be a wrapped set of elements. Therefore a call to

this.each(function(){
});

within the hook should be more save for checking. That way you have an exact knowledge of when an object is removed without an intervall timer.

Combining the various suggestions here is as simplified version which should work regardless of the scope in which it is defined.

function showLoader () {
    $('#mc_signup_form').prepend('<span class="loading"> loading &hellip;</span>');
    setTimeout (function check_trigger () {
      if ( $('.mc_error_msg').length == 0 || $('.mc_success_msg').length == 0 ) {
        $('#mc_signup_form .loading').remove();
      } else {
        setTimeout (check_trigger, 300);
      }   
    }, 300); 
}

I find passing strings to setTimeout and setInterval just leads to problems :)

Try:

setInterval(check_trigger, 300);

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