How do I get the position of an element after css3 translation in JavaScript?

I saw this posted in 2 different forms on stackoverflow, but the solutions don't work for me.

Essentially, I have an item that I will translate. When I do a obj.style.left or obj.offsetLeft, after the element has been translated, I get 0. Is there anyway I can get the coordinates/position of an element after it has been translated with css3?

I can't use jQuery (because I can't and also because I want to understand the solution, not just use the library without understanding what is happening underneath)

Any ideas?

Thanks much!

Answers:

Answer

You can use getBoundingClientRect():

Imagine the following html block:

<div class="centralizer popup">
    <div class="dragger"></div>
</div>

And the style:

body {
    background:#ccc;
}
.centralizer {
    position:absolute;
    top:150px;
    left:170px;
    width:352px;
    height:180px;
    overflow:auto;
    -webkit-transform: translateY(-50%) translateX(-50%);
    -moz-transform: translateY(-50%) translateX(-50%);
    -ms-transform: translateY(-50%) translateX(-50%);
    transform: translateY(-50%) translateX(-50%);
}
.popup {
    background:white;
    box-shadow:0 0 0 2px rgba(0, 0, 0, 0.1), 0 0 15px rgba(0, 0, 0, 0.3);
    border-radius:3px;
}
.dragger {
    background:#eee;
    height:35px;
    border-radius:3px 3px 0 0;
    border-bottom:1px solid #ccc;
}

Now you can use the following javascript to get the correct position:

var popup = document.querySelector('.popup');
var rect = popup.getBoundingClientRect();

console.log("popup.getBoundingClientRect(): \n" + "x: " + rect.left + "\ny: " + rect.top);

You can check the result in the jsfiddle:

I tested on FF, IE and chrome, and it worked on all my tests.

Answer

Ok, hold tight because this is not nice:

window.addEventListener('load', function(){
  var node = document.getElementById("yourid");
  var curTransform = new   WebKitCSSMatrix(window.getComputedStyle(node).webkitTransform);
  console.log(node.offsetLeft + curTransform.m41); //real offset left
  console.log(node.offsetTop + curTransform.m42); //real offset top
});

You can play with it here:

http://jsfiddle.net/duopixel/wzZ5R/

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