textualRatio.js

var textualRatio = (function () {
    var
            isInteger,
            greatestCommonDivisor;

    /**
     *
     * @param value
     * @returns {boolean}
     */
    isInteger = function (value) {
        return !!/^[0-9]+$/.test(value);
    };

    /**
     *
     * Greatest Common Divisor
     * @param {number} a
     * @param {number} b
     * @returns {number}
     */
    greatestCommonDivisor = function (a, b) {
        if (b === 0) return a;
        return greatestCommonDivisor(b, a % b);
    };

    /**
     * Reduce a numerator and denominator to it's smallest, integer ratio using Euclid's Algorithm
     * @param {number|string} numerator
     * @param {number|string} denominator
     * @returns {string}
     */
    return function (numerator, denominator) {
        var divisor, temp;
        if (!isInteger(numerator) || !isInteger(denominator)) {
            return '?:?';
        }
        else if (numerator === denominator) {
            return '1:1';
        }
        else if (+numerator < +denominator) {
            temp = numerator;
            numerator = denominator;
            denominator = temp;
        }
        divisor = greatestCommonDivisor(+numerator, +denominator);
        return 'undefined' === typeof temp
                ? (numerator / divisor) + ':' + (denominator / divisor)
                : (denominator / divisor) + ':' + (numerator / divisor);
    }
})();