Jquery – How to run a directive after the dom has finished rendering

angularjscallbackdocument-readydomjquery

I've got a seemingly simple problem with no apparent (by reading the Angular JS docs) solution.

I have got an Angular JS directive that does some calculations based on other DOM elements' height to define the height of a container in the DOM.

Something similar to this is going on inside the directive:

return function(scope, element, attrs) {
    $('.main').height( $('.site-header').height() -  $('.site-footer').height() );
}

The issue is that when the directive runs, $('site-header') cannot be found, returning an empty array instead of the jQuery wrapped DOM element I need.

Is there a callback that I can use within my directive that only runs after the DOM has been loaded and I can access other DOM elements via the normal jQuery selector style queries?

Best Answer

It depends on how your $('site-header') is constructed.

You can try to use $timeout with 0 delay. Something like:

return function(scope, element, attrs) {
    $timeout(function(){
        $('.main').height( $('.site-header').height() -  $('.site-footer').height() );
    });        
}

Explanations how it works: one, two.

Don't forget to inject $timeout in your directive:

.directive('sticky', function($timeout)

How to use:

You can be sure that the function given above returns correct answer at the moment of time when it is called, but what about tracking element's visibility as an event?

Place the following code at the bottom of your <body> tag:

function onVisibilityChange(el, callback) {
    var old_visible;
    return function () {
        var visible = isElementInViewport(el);
        if (visible != old_visible) {
            old_visible = visible;
            if (typeof callback == 'function') {
                callback();
            }
        }
    }
}

var handler = onVisibilityChange(el, function() {
    /* Your code go here */
});


// jQuery
$(window).on('DOMContentLoaded load resize scroll', handler);

/* // Non-jQuery
if (window.addEventListener) {
    addEventListener('DOMContentLoaded', handler, false);
    addEventListener('load', handler, false);
    addEventListener('scroll', handler, false);
    addEventListener('resize', handler, false);
} else if (window.attachEvent)  {
    attachEvent('onDOMContentLoaded', handler); // Internet Explorer 9+ :(
    attachEvent('onload', handler);
    attachEvent('onscroll', handler);
    attachEvent('onresize', handler);
}
*/

If you do any DOM modifications, they can change your element's visibility of course.

Guidelines and common pitfalls:

Maybe you need to track page zoom / mobile device pinch? jQuery should handle zoom/pinch cross browser, otherwise first or second link should help you.

If you modify DOM, it can affect the element's visibility. You should take control over that and call handler() manually. Unfortunately, we don't have any cross browser onrepaint event. On the other hand that allows us to make optimizations and perform re-check only on DOM modifications that can change an element's visibility.

Never Ever use it inside jQuery $(document).ready() only, because there is no warranty CSS has been applied in this moment. Your code can work locally with your CSS on a hard drive, but once put on a remote server it will fail.

After DOMContentLoaded is fired, styles are applied, but the images are not loaded yet. So, we should add window.onload event listener.

We can't catch zoom/pinch event yet.

The last resort could be the following code:

/* TODO: this looks like a very bad code */
setInterval(handler, 600);

You can use the awesome feature pageVisibiliy of the HTML5 API if you care if the tab with your web page is active and visible.

TODO: this method does not handle two situations:

Overlapping using z-index.
Using overflow-scroll in element's container.
Try something new - The Intersection Observer API explained.

Javascript – How to find event listeners on a DOM node in JavaScript or in debugging

If you just need to inspect what's happening on a page, you might try the Visual Event bookmarklet.

Update: Visual Event 2 available.

Best Answer

Related Solutions

Javascript – How to tell if a DOM element is visible in the current viewport

How to use:

Javascript – How to find event listeners on a DOM node in JavaScript or in debugging

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