css transitions on new elements

I cannot find a way to use css transitions on newly created dom elements.

let's say I have an empty html document.

<body>
    <p><a href="#" onclick="return f();">click</a></p>
</body>

I also have this css

#id {
    -moz-transition-property: opacity;
    -moz-transition-duration: 5s;
    opacity: 0;
}

#id.class {
    opacity: 1;
}

and this js

function f() {
    var a = document.createElement('a');
    a.id = 'id';
    a.text = ' fading in?';
    document.getElementsByTagName('p')[0].appendChild(a);
    // at this point I expect the span element to be with opacity=0

    a.className = 'class';
    // now I expect the css transition to go and "fade in" the a        

    return false;
}

but, as you can see on http://jsfiddle.net/gwxkW/1/ when you click the element appears instantaneously.

If I try to set the class in a timeout() i often find the result, but to me it seems more a race between javascript and the css engine. Is there some specific event to listen? I tried to use document.body.addEventListener('DOMNodeInserted', ...) but it's not working.

How can I apply css transitions on newly created elements?

requestAnimationFrame() (https://developer.mozilla.org/en-US/docs/Web/API/window.requestAnimationFrame) appears to work across Firefox, Chrome and Safari. A more reliable, logical solution that setTimeout(). For older browsers (IE8), it will require a Polyfill (naturally, the transition won't occur, but the CSS will still change).

In Firefox, it does appear to be a race between layout completing and the CSS transition. Chrome is much more predictable. If I set the class name on a setTimeout(), Chrome always works, Firefox only works if the setTimeout() time is long.

With this code in Firefox (even using the setTimeout()), the text shows immediately:

function f() {
    var a = document.createElement('a');
    a.id = 'id';
    a.innerHTML = ' fading in?';
    document.getElementsByTagName('p')[0].appendChild(a);
    // at this point I expect the span element to be with opacity=0

    setTimeout(function() {
        a.className = 'fadeIn';
    }, 10);
    return false;
}

But, if I force a reflow by requesting a property that can only be returned after layout, it then starts to work in Firefox:

function f() {
    var a = document.createElement('a');
    a.id = 'id';
    a.innerHTML = ' fading in?';
    document.getElementsByTagName('p')[0].appendChild(a);
    // at this point I expect the span element to be with opacity=0

    // request property that requires layout to force a layout
    var x = a.clientHeight;
    setTimeout(function() {
        a.className = 'fadeIn';
    }, 10);
    return false;
}

Furthermore, once I've request that property to force a layout, I can even remove the setTimeout() and the animation works in Firefox.

function f() {
    var a = document.createElement('a');
    a.id = 'id';
    a.innerHTML = ' fading in?';
    document.getElementsByTagName('p')[0].appendChild(a);
    // at this point I expect the span element to be with opacity=0

    // request property that requires layout to force a layout
    var x = a.clientHeight;
    a.className = 'fadeIn';
    return false;
}

You can see this last one work here in both Chrome and Firefox: http://jsfiddle.net/jfriend00/phTdt/

And, here's an article that discusses the phenomenon: http://gent.ilcore.com/2011/03/how-not-to-trigger-layout-in-webkit.html

demian85

I found a nicer way to trigger layout and make transitions work just after appending the element to the DOM:

window.getComputedStyle(element).opacity;

来源：https://stackoverflow.com/questions/12088819/css-transitions-on-new-elements

标签

javascript

css

firefox

css3

css-transitions