How to get margin value of a div in plain JavaScript?

I found something very useful on this site when I was searching for an answer on this question. You can check it out at http://www.codingforums.com/javascript-programming/230503-how-get-margin-left-value.html. The part that helped me was the following:

/***
 * get live runtime value of an element's css style
 *   http://robertnyman.com/2006/04/24/get-the-rendered-style-of-an-element
 *     note: "styleName" is in CSS form (i.e. 'font-size', not 'fontSize').
 ***/
var getStyle = function(e, styleName) {
  var styleValue = "";
  if (document.defaultView && document.defaultView.getComputedStyle) {
    styleValue = document.defaultView.getComputedStyle(e, "").getPropertyValue(styleName);
  } else if (e.currentStyle) {
    styleName = styleName.replace(/\-(\w)/g, function(strMatch, p1) {
      return p1.toUpperCase();
    });
    styleValue = e.currentStyle[styleName];
  }
  return styleValue;
}
////////////////////////////////////
var e = document.getElementById('yourElement');
var marLeft = getStyle(e, 'margin-left');
console.log(marLeft);    // 10px

#yourElement {
  margin-left: 10px;
}

<div id="yourElement"></div>

The properties on the style object are only the styles applied directly to the element (e.g., via a style attribute or in code). So .style.marginTop will only have something in it if you have something specifically assigned to that element (not assigned via a style sheet, etc.).

To get the current calculated style of the object, you use either the currentStyle property (Microsoft) or the getComputedStyle function (pretty much everyone else).

Example:

var p = document.getElementById("target");
var style = p.currentStyle || window.getComputedStyle(p);

display("Current marginTop: " + style.marginTop);

Fair warning: What you get back may not be in pixels. For instance, if I run the above on a p element in IE9, I get back "1em".

Live Copy | Source

Also, you can create your own outerHeight for HTML elements. I don't know if it works in IE, but it works in Chrome. Perhaps, you can enhance the code below using currentStyle, suggested in the answer above.

Object.defineProperty(Element.prototype, 'outerHeight', {
    'get': function(){
        var height = this.clientHeight;
        var computedStyle = window.getComputedStyle(this); 
        height += parseInt(computedStyle.marginTop, 10);
        height += parseInt(computedStyle.marginBottom, 10);
        height += parseInt(computedStyle.borderTopWidth, 10);
        height += parseInt(computedStyle.borderBottomWidth, 10);
        return height;
    }
});

This piece of code allow you to do something like this:

document.getElementById('foo').outerHeight

According to caniuse.com, getComputedStyle is supported by main browsers (IE, Chrome, Firefox).