[javascript] Get css top value as number not as string?

In jQuery you can get the top position relative to the parent as a number, but you can not get the css top value as a number if it was set in px.
Say I have the following:

#elem{
  position:relative;
  top:10px;
 }

<div>
  Bla text bla this takes op vertical space....
  <div id='elem'>bla</div>
</div>

$('#elem').position().top; //Returns the number (10+(the vertical space took by the text))
$('#elem').css('top'); //Returns the string '10px'

But I want to have the css top property as the number 10.
How would one achieve this?

A jQuery plugin based on M4N's answer

jQuery.fn.cssNumber = function(prop){
    var v = parseInt(this.css(prop),10);
    return isNaN(v) ? 0 : v;
};

So then you just use this method to get number values

$("#logo").cssNumber("top")

A slightly more practical/efficient plugin based on Ivan Castellanos' answer (which was based on M4N's answer). Using || 0 will convert Nan to 0 without the testing step.

I've also provided float and int variations to suit the intended use:

jQuery.fn.cssInt = function (prop) {
    return parseInt(this.css(prop), 10) || 0;
};

jQuery.fn.cssFloat = function (prop) {
    return parseFloat(this.css(prop)) || 0;
};

Usage:

$('#elem').cssInt('top');    // e.g. returns 123 as an int
$('#elem').cssFloat('top');  // e.g. Returns 123.45 as a float

Test fiddle on http://jsfiddle.net/TrueBlueAussie/E5LTu/

A jQuery plugin based on M4N's answer

jQuery.fn.cssNumber = function(prop){
    var v = parseInt(this.css(prop),10);
    return isNaN(v) ? 0 : v;
};

So then you just use this method to get number values

$("#logo").cssNumber("top")

A slightly more practical/efficient plugin based on Ivan Castellanos' answer (which was based on M4N's answer). Using || 0 will convert Nan to 0 without the testing step.

I've also provided float and int variations to suit the intended use:

jQuery.fn.cssInt = function (prop) {
    return parseInt(this.css(prop), 10) || 0;
};

jQuery.fn.cssFloat = function (prop) {
    return parseFloat(this.css(prop)) || 0;
};

Usage:

$('#elem').cssInt('top');    // e.g. returns 123 as an int
$('#elem').cssFloat('top');  // e.g. Returns 123.45 as a float

Test fiddle on http://jsfiddle.net/TrueBlueAussie/E5LTu/