Converting colors or numbers from Hex to Dec

Recently, I needed to create a function that fades from one color to the other. CSS3 makes the job very easy by making use of the transition property. However I needed to use this functionality inside a canvas element, meaning I would have to calculate the transition in JavaScript.

CSS3 Method:

.selector {
    color:red;
    transition: color .5s;
}
.selector:hover {
color:green;
}

On the browsers, colors can be set using 3 types of notations: RGB, HEX, or HSL. I usually prefer using HEX notation (#34B620) but the only problem is I'd have to convert these numbers into integers I can manage first before I can animate a transition.

HEX to DEC

The numbers #34B620 need to be translated into rgb(52, 182, 32). To do so, we can create a function that convert Hex into integers.

function convertColor(hexa){
    var chunks = [];
    var tmp,i;
    hexa = hexa.substr(1); // remove the pound 
    if ( hexa.length === 3){
        tmp = hexa.split("");
        for(i=0;i<3;i++){
            chunks.push(parseInt(tmp[i]+""+tmp[i],16));
        }
    }else if (hexa.length === 6){
        tmp = hexa.match(/.{2}/g);
        for(i=0;i<3;i++){
            chunks.push(parseInt(tmp[i],16));
        }
    }else {
        throw new Error("'"+hexa+"' is not a valid hex format");
    }

    return chunks;
}

This function can properly convert hexadecimal numbers if they come in 3 digit format and 6 digit format.

convertColor("#00FF00");
// [0, 255, 0]

convertColor("#0639FF");
// [6, 57, 255]

convertColor("#06D");
// [0, 102, 221]

Now that I have integers I can work with, I can easily create a transition from color to color.

DEC to HEX

The opposite is much easier to do. We can simply call a .toString() method with the argument 16 for hex on a number.

var decnumber = 12;
var hexnumber = decnumber.toString(16);
// C

To convert the colors to hex we can simply loop through the values we converted earlier and call toString():

function convertToHexColor(decArray){
    var i,l = decArray.length,
    hexColor = "#";

    for (i=0;i<l;i++){
        hexColor += decArray[i].toString(16);
    }
    return hexColor;
}

That's it, we now know how to convert from hex to dec and from dec to hex using JavaScript.