How to get the CSS left-property value of a div using JavaScript

Question

My CSS rule looks like this:

#my-div{
    display: none;
    position: absolute;
    left: -160px;
    bottom: -150px;
}

I'm trying to get value of the left-property like this:

• document.getElementById('my-div').style.left
• document.getElementById('my-div').offsetLeft

The problem is that both return null. Where is the problem?

Answer 1

The problem is that someElement.style.left only work if you have inline style. Since you apply your styling through a stylesheet, you will not be able to fetch the value the way you expect.

You have a couple of other approaches you could take to get the value through JavaScript:

window.getComputedStyle:

It is possible to get the computed style of an element using window.getComputedStyle, the problem is that it has quite limited support (IE9+). If you still want to use it you could wrap it up in a function to make it a bit easier to get each property:

function getCssProperty(elmId, property){
   var elem = document.getElementById(elmId);
   return window.getComputedStyle(elem,null).getPropertyValue(property);
}
// You could now get your value like
var left = getCssProperty("my-div", "left");

Working example

jQuery (or some other library):

Another option would be to use a JavaScript library like jQuery (or whatever you prefer), which will provide you with a cross-browser solution to get the value.

With jQuery you could use the .css() method to read the CSS-property of the element.

$(function () {
  var left = $("#my-div").css("left");
});

Working example ​

Answer 2

You should call this

document.getElementById('my-div').style.left
document.getElementById('my-div').offsetLeft

when document is loaded, if you call it earlier it will return null because element doesnt exists yet. So you can use jQuery to determine when all content is loaded.

$(function() {
    //put your code here
});