parsing css measures

Question

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 function:

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.

Note that giving three values (e.g. "10px 5px 7px") is perfectly valid; the 1st value is for the top, the 2nd is for the left & right, the 3rd for the bottom. — outis
– outis, Commented Apr 19, 2010 at 23:01

user187291 · Accepted Answer · 2010-04-19 23:10:49Z

8

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]

answered Apr 19, 2010 at 23:10

user187291

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Comments

outis · Accepted Answer · 2010-04-19 23:46:43Z

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'};
    })
}

edited Apr 19, 2010 at 23:46

answered Apr 19, 2010 at 23:06

outis

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2 Comments

meo Over a year ago

the case solution is definitely better. But what if the unit is not px but em or %? And what is the "?" doing (matches[2] ? matches[2])

outis Over a year ago

The unit group (.*) will match any characters. In particular, the first group will match all the digits and the remaining characters will be the unit. The ? isn't alone; it's part of the lone ternary operator, ?:. It's like an 'if-else', but as an expression rather than a statement. It ensures that the value has valid units; if no units were specified, the units default to 'px'. Search SO for "ternary" for more information.

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