Cross-browser (IE8-) getComputedStyle with Javascript?

Question

Since IE8 does not support getComputedStyle, we can only use currentStyle. However, it does not return the real "computed" value for some properties.

For example:

<style type="text/css">
#div {/* no properties are defined here */}
</style>

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

// returns "medium" instead of 0px
document.getElementById('div').currentStyle.borderLeftWidth

// returns "auto" instead of 0px
document.getElementById('div').currentStyle.marginLeft

// returns "undefined" instead of 1
document.getElementById('div').currentStyle.opacity

Does anyone have a cross-browser solution for all properties without using jQuery or other Javascript libraries?

Answer 1

Here's a cross-browser function to get a computed style...

getStyle = function (el, prop) {
    if (typeof getComputedStyle !== 'undefined') {
        return getComputedStyle(el, null).getPropertyValue(prop);
    } else {
        return el.currentStyle[prop];
    }
}

You may store it as an utility within an object, or just use it as provided. Here's a sample demo!

// Create paragraph element and append some text to it
var p = document.createElement('p');
p.appendChild(document.createTextNode('something for fun'));

// Append element to the body
document.getElementsByTagName('body')[0].appendChild(p);

// Set hex color to this element
p.style.color = '#999';

// alert element's color using getStyle function
alert(getStyle(p, 'color'));

Check this demo to see it in action:

getStyle = function(el, prop) {
  if (getComputedStyle !== 'undefined') {
    return getComputedStyle(el, null).getPropertyValue(prop);
  } else {
    return el.currentStyle[prop];
  }
}

// Create paragraph element and append some text to it
var p = document.createElement('p');
p.appendChild(document.createTextNode('something for fun'));

// Append element to the body
document.getElementsByTagName('body')[0].appendChild(p);

// Set hex color to this element
p.style.color = '#999';

// alert element's color using getStyle function
console.log(getStyle(p, 'color'));

p {
  color: red;
}