How can I determine the background image url of a div via javascript?

Question

I've found plenty of information on how to change the background image of a div using Javascript, but I am trying to use Javacript to determine which background image is being displayed. The code to set the image goes like this:

document.getElementById("widgetField").style.background="url(includes/images/datepicker_open.png)";

I have tried every combination I can think of to access the background image url, but so far no dice:

alert(document.getElementById("widgetField").style.backgroundImage.url);  - returns Undefined
alert(document.getElementById("widgetField").style.backgroundImage);  - empty response
alert(document.getElementById("widgetField").style.background);
alert(document.getElementById("widgetField").style.background.image);
alert(document.getElementById("widgetField").style.background.url);
alert(document.getElementById("widgetField").style.background.image.url);
alert(document.getElementById("widgetField").style.background.value);
alert(document.getElementById("widgetField").style.background.image.value);
alert(document.getElementById("widgetField").style.background.image.value);
alert(document.getElementById("widgetField").style.backgroundImage.value);

Does anyone know how to do this? Is it possible?

BTW, here is the way the image is being set in CSS in the beginning:

#widgetField {
    width: 290px;
    height: 26px;
    background: url(../images/datepicker_closed.png);
    overflow: hidden;
    position: relative;
}

UPDATE:

If I run the following, it works:

document.getElementById("widgetField").style.background="url(includes/images/datepicker_open.png)";
alert(document.getElementById("widgetField").style.background);

However, I cannot seem to access the URL property until it has been set by Javascript, even though it is already defined in the CSS file. Is there a reason why the raw CSS setting is not accessible?

Answer 1

You're setting the background property, background and backgroundImage are two seperate properties which is why backgroundImage is empty after setting background. If you want to access just the url part of the background property, you can use the following code:

var wfBg = document.getElementById("widgetField").style.background;
var wfBgUrl = wfBg.match(/(url\(['"]?([^)])['"]?\))/i;

if (wfBgUrl)
{
    // Add your code here. wfBgUrl[1] is full string including "url()", 
    // wfBgUrl[2] would be just the url inside the parenthesis
}

For styles set by css documents:

if (window.getComputedStyle) // For standards compliant browsers
    var wfBg = window.getComputedStyle(
        document.getElementById("widgetField")
    ).getPropertyValue("background");
else // for IE
    var wfBg = document.getElementById("widgetField").currentStyle.background;

Answer 2

Get the background property:

alert(document.getElementById("widgetField").style.background);

Displays : url(includes/images/datepicker_open.png)

Edit: Andy E's answer should be close to what you need. One difference is that for IE you need

currentStyle.backgroundImage 

instead of

currentStyle.background

Answer 3

this should do it

alert( document.getElementById("widgetField").style['background-image'] );

You can do the following to get all the style properties after you have made changes ... so you see where the new things went ...

  var style = document.getElementById("widgetField").style;
  var allprops = '';
  for  ( i in style )
    allprops += style[i] + ':' + i + '\n' ;
  alert( allprops );

[EDIT] as i go along i will add here ..
Google Chrome: style['background-image']
Firefox 3.5.7: style.background
IE 6: style.background

style.backgroundImage work on all browsers ( IE6, IE7, FF 3.5.7, Google Chrome, Opera 10.10, Safari 4.0.4) for Windows ..

Answer 4

Try this:

var img = document.getElementById('widgetField'),
style = img.currentStyle || window.getComputedStyle(img, false),
bi = style.backgroundImage.slice(4, -1);