parsing css measures

When i write a jQuery plugin i like to specify options for spacings the CSS way. I wrote a function that returns a CSS String as values in a object.

5px 10px returns top: 5px, right: 10px, bottom: 5px, left: 10px

Now i often use the returned values to do some calculations and its not very nice to have to extract the measuring unit every time...

I suck in writing regular expressions could someone help me complete this funct开发者_JAVA技巧ion:

this.cssMeasure = function(cssString, separateUnits){

    if ( cssString ){
        var values = {}
    }else{
        return errorMsg
    }

    var spacing = cssString.split(' ')
    var errorMsg = 'please format your css values correctly dude'

    if( spacing[4] ) {
        return errorMsg
    } else if ( spacing[3] ) {
        values = {top: spacing[0], right:spacing[1], bottom:spacing[2], left:spacing[3]}
    } else if ( spacing[2] ) {
        values = {top: spacing[0], right:spacing[1], bottom:spacing[2], left:spacing[1]} 
    } else if ( spacing[1] ) {
        values = {top: spacing[0], right:spacing[1], bottom:spacing[0], left:spacing[1]}
    } else {
        values = {top: spacing[0], right:spacing[0], bottom:spacing[0], left:spacing[0]}
    }

    if (separateUnits) {
        $.each(values, function(i, value){
            /*
             at this place i need to extract the measuring unit of each value and return them separately
             something like top: {value: 10, unit: 'px'}, right: {bla} and so on
            */
        })
    }

    return values

}

if you have any idea how to improve this function i am open to your comments.

According to http://www.w3.org/TR/css3-values/#ltnumbergt , "A number can either be an integer, or it can be zero or more digits followed by a dot (.) followed by one or more digits", in regexp language

\d+|\d*\.\d+

Let's add an optional sign to it, and make the group "non-capturing" to make the parsing simpler

([+-]?(?:\d+|\d*\.\d+))

Enumerating all possible units is tedious, therefore let the unit be any sequence of lowercase letters (including none) or a percent sign

([a-z]*|%)

Putting it all together,

propRe = /^([+-]?(?:\d+|\d*\.\d+))([a-z]*|%)$/

When you apply this to a value

  parts = "+12.34em".match(propRe)

the numeric value will be in parts[1] and the unit in parts[2]

switch (spacing.length) {
case 1:
    values = {top: spacing[0], right:spacing[0], bottom:spacing[0], left:spacing[0]};
    break;
case 2:
    values = {top: spacing[0], right:spacing[1], bottom:spacing[0], left:spacing[1]};
    break;
case 3:
    values = {top: spacing[0], right:spacing[1], bottom:spacing[2], left:spacing[1]};
    break;
case 4:
    values = {top: spacing[0], right:spacing[1], bottom:spacing[2], left:spacing[3]};
    break;
default:
    return errorMsg;
}

if (separateUnits) {
    values = $.map(values, function(i, value){
        matches = value.match(/([-+]?[\d.]*)(.*)/);
        return {value: matches[1]+0, 
                unit: matches[2] ? matches[2] : 'px'};
    })
}