mega_number.js

    function(number, fractionSize) {
        if (number === null) return null;
        if (number === 0) return "0";

        if (!fractionSize || fractionSize < 0) fractionSize = 1;

        var abs = Math.abs(number);
        var rounder = Math.pow(10, fractionSize);
        var isNegative = number < 0;
        var key = "";
        var powers = [
            { key: "Q", value: Math.pow(10, 15) },
            { key: "T", value: Math.pow(10, 12) },
            { key: "B", value: Math.pow(10, 9) },
            { key: "M", value: Math.pow(10, 6) },
            { key: "K", value: 1000 }
        ];

        for (var i = 0; i < powers.length; i++) {
            var reduced = abs / powers[i].value;

            reduced = Math.round(reduced * rounder) / rounder;

            if (reduced >= 1) {
                abs = reduced;
                key = powers[i].key;
                break;
            }
        }

        return (isNegative ? "-" : "") + abs + key;
    };