My ghetto frame counter (for tracking fps), now replaced with mrdoob's Stats.js

framecounter.js

function FrameCounter(sample_length) {
    this.sample_length = sample_length || 500; // In milliseconds
    this.n = 0;
    this.last_n = 0;
    this.time_created = this.time_sampled = this.time_updated = new Date();
    this.last_rate = 0;
}
FrameCounter.prototype = {
    tick: function() {
        this.n++;
        this.time_updated = +new Date();
    },
    get_rate: function() {
        var now = +new Date();
        var delta = now - this.time_sampled;
        if(delta < this.sample_length) return this.last_rate;
        this.last_rate = (this.n - this.last_n) / delta;
        this.last_n = this.n;
        this.time_sampled = now;
        return this.last_rate * 1000;
    },
    get_time_elapsed: function() {
        return new Date() - this.time_created;
    }
}