Calculate the aspect ratio given a width and a height

aspect-ratio.js

// calculate the aspect ration given a width and a height
function aspectRatio(width, height) {
    // calculate the greates common denominator of two numbers
    function gcd(a, b) {
        if (b === 0) {
        return a;
        }
        return gcd(b, a % b);
    }
    var gcdValue = gcd(width, height);
    return width / gcdValue + ':' + height / gcdValue;
}