What Is the Most Efficient Way to Parse a CSS Color in JavaScript

What is the most efficient way to parse a CSS color in JavaScript?

function parseColor(input) {
    var m;

Obviously, the numeric values will be easier to parse than names. So we do those first.

    m = input.match(/^#([0-9a-f]{3})$/i)[1];
    if( m) {
        // in three-character format, each value is multiplied by 0x11 to give an
        // even scale from 0x00 to 0xff
        return [
            parseInt(m.charAt(0),16)*0x11,
            parseInt(m.charAt(1),16)*0x11,
            parseInt(m.charAt(2),16)*0x11
        ];
    }

That's one. Now for the full six-digit format:

    m = input.match(/^#([0-9a-f]{6})$/i)[1];
    if( m) {
        return [
            parseInt(m.substr(0,2),16),
            parseInt(m.substr(2,2),16),
            parseInt(m.substr(4,2),16)
        ];
    }

And now for rgb() format:

    m = input.match(/^rgb\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*\)$/i);
    if( m) {
        return [m[1],m[2],m[3]];
    }

Optionally, you can also add support for rgba format, and even hsl/hsla if you add an HSL2RGB conversion function.

Finally, the named colours.

    return ({
        "red":[255,0,0],
        "yellow":[255,255,0],
        // ... and so on. Yes, you have to define ALL the colour codes.
    })[input];

And close the function:

}

---

Actually, I don't know why I bothered writing all that. I just noticed you specified "assuming a major browser", I'm assuming that also means "up-to-date"? If so...

function parseColor(input) {
    var div = document.createElement('div'), m;
    div.style.color = input;
    m = getComputedStyle(div).color.match(/^rgb\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*\)$/i);
    if( m) return [m[1],m[2],m[3]];
    else throw new Error("Colour "+input+" could not be parsed.");
}

An up-to-date browser will convert any given colour to rgb() format in its computed style. Just get it back, and read it out.

Parsing CSS in JavaScript / jQuery

There is a CSS parser written in Javascript called JSCSSP

How to extract r, g, b, a values from CSS color?

var c = $('body').css('background-color');
var rgb = c.replace(/^(rgb|rgba)\(/,'').replace(/\)$/,'').replace(/\s/g,'').split(',');

for(var i in rgb) {
  console.log(rgb[i]);
}

Try it here http://jsbin.com/uhawa4

Edit :

var c = $('body').css('background-color');
var rgb = c.replace(/^rgba?\(|\s+|\)$/g,'').split(',');

for(var i in rgb) {
  console.log(rgb[i]);
}

or even simpler way, just aiming at numbers

var c = 'rgba(60,4,2,6)';
var rgb = c.match(/\d+/g);

for(var i in rgb) {
  console.log(rgb[i]);
}

How do you read CSS rule values with JavaScript?

Adapted from here, building on scunliffe's answer:

function getStyle(className) {
    var cssText = "";
    var classes = document.styleSheets[0].rules || document.styleSheets[0].cssRules;
    for (var x = 0; x < classes.length; x++) {        
        if (classes[x].selectorText == className) {
            cssText += classes[x].cssText || classes[x].style.cssText;
        }         
    }
    return cssText;
}

alert(getStyle('.test'));

---

Related Topics