Make a number into rounded text in quasi-engineering notation. Idea taken from Facebook Like count display.

bigRound

function bigRound(num, prcn) {
    if (num < 1000) {
        return num;
    };
    var rndup = 0.000001;
    var sfxs = ['k', 'M', 'B', 'T', 'Q'];
    var expt = Math.floor(Math.log(num) / Math.LN10 + rndup);
    var sfx = sfxs[Math.floor(expt / 3) - 1];
    var clip = +(num * 1.0 / Math.pow(10, expt - expt % 3)).toPrecision(prcn || 2);
    return clip + sfx;
}

rndup fixes a javascript float-representation rounding error.

Possible future enhancement: small numbers as well, but this would make it kind of clunky to use B for billion, T for trillion, and up instead of their real metric prefixes.

[ ... , 'n', 'μ', 'm', '', 'k', 'M', 'G', ... ]