Simple JS Perf Timer API

perf.js

/**
 * perf.js
 * Simple JS Timer API
 * 
 * @public
 * @param {number} alpha weight for EWMA trends (default: 0.2)
 * @this {Perf}
 * @constructor
 */
var Perf = function(alpha) {

	"use strict";

	// private members ----------

	// bound alpha within 0-1, default to 0.2
	alpha = (alpha > 0) ? ((alpha < 1) ? alpha : 1) : 0.2;

	/**
	 * Date.now() polyfill
	 * 
	 * @private
	 * @type {function()}
	 */
	var now = Date.now || function() { return new Date().getTime(); };

	/**
	 * Starting clock (ms since UNIX epoch)
	 * 
	 * @private
	 * @type {Object}
	 */
	var start = {};

	/**
	 * Most recent measurement
	 * 
	 * @private
	 * @type {number}
	 */
	var last = 0;

	/**
	 * Sum of measurements
	 * 
	 * @private
	 * @type {number}
	 */
	var sum = 0;

	/**
	 * Count of measurements
	 * 
	 * @private
	 * @type {number}
	 */
	var count = 0;

	/**
	 * Exponentially Weighted Moving Average
	 * 
	 * @private
	 * @type {number}
	 */
	var ewma = 0;

	// public members ----------

	return {
		/**
		 * Gets most recent timing in ms
		 * 
		 * @public
		 * @param {number} digits the number of digits for formatting
		 * @return {string}
		 */
		last: function(digits) {
			return last.toFixed(digits || 0);
		},

		/**
		 * Gets the average timing in ms
		 * 
		 * @public
		 * @param {number} digits the number of digits for formatting
		 * @return {string}
		 */
		mean: function(digits) {
			return (count ? (sum / count) : 0).toFixed(digits || 0);
		},

		/**
		 * Gets sum of all timings in ms
		 * 
		 * @public
		 * @param {number} digits the number of digits for formatting
		 * @return {string}
		 */
		sum: function(digits) {
			return sum.toFixed(digits || 0);
		},

		/**
		 * Gets weighted timing trend in ms
		 * 
		 * @public
		 * @param {number} digits the number of digits for formatting
		 * @return {string}
		 */
		trend: function(digits) {
			return ewma.toFixed(digits || 0);
		},

		/**
		 * Begins timing
		 * 
		 * @public
		 */
		start: function(key) {
			start[key || ''] = now();
		},

		/**
		 * Ends timing
		 * 
		 * @public
		 */
		stop: function(key) {
			key = key || '';
			if (!start[key]) { return; }

			// last
			last = now() - start[key];
			delete start[key];

			// exponentially weighted moving average
			ewma = count ? (alpha*last) + ((1-alpha)*ewma) : last;

			// mean
			sum += last;
			count++;
		},

		/**
		 * Ends timing but doesn't record
		 * 
		 * @public
		 */
		cancel: function(key) {
			key = key || '';
			if (!start[key]) { return; }

			delete start[key];
		},

		/**
		 * Clears all statistics
		 * 
		 * @public
		 */
		reset: function() {
			start = {};
			last = sum = count = ewma = 0;
		},

		/**
		 * Creates a unique key
		 * 
		 * @public
		 */
		unique: function() {
			return (now()+Math.random()).toString(36);
		}
		
	};
};

perf.min.js

var Perf=function(c){var c=0<c?1>c?c:1:0.2,h=Date.now||function(){return(new Date).getTime()},b={},d=0,e=0,f=0,g=0;return{last:function(a){return d.toFixed(a||0)},mean:function(a){return(f?e/f:0).toFixed(a||0)},sum:function(a){return e.toFixed(a||0)},trend:function(a){return g.toFixed(a||0)},start:function(a){b[a||""]=h()},stop:function(a){a=a||"";b[a]&&(d=h()-b[a],delete b[a],g=f?c*d+(1-c)*g:d,e+=d,f++)},cancel:function(a){a=a||"";b[a]&&delete b[a]},reset:function(){b={};d=e=f=g=0},unique:function(){return(h()+
Math.random()).toString(36)}}};