duration.js

function duration(timeInMillis) {
    var intervals = {
            'h': 3600000,
            'm': 60000,
            's': 1000,
            'ms': 1
        },
        sb = '';
        
    for (var k in intervals) {
        if (!intervals.hasOwnProperty(k)) continue;

        var v = intervals[k],
            unit = Math.floor(timeInMillis / v);
        timeInMillis %= v;
        
        if (unit > 0 || (sb.length === 0 && k === 'ms')) {
            if (sb.length > 0) sb += ':';
            sb += unit + k;
        }
    }
    return sb;
}