SubtleBenchmarker.js

var SubtleBenchmarker = new new Class({
	
	benchmarks:{},
	
	start : function(key){
		this.benchmarks[key] = this.benchmarks[key] || [];
		this.benchmarks[key].push({ start:new Date() });
	},
	end : function(key){
		this.benchmarks[key][this.benchmarks[key].length-1].end = new Date();
	},
	
	report: function(key){
		var report = {};
		Hash.each(this.benchmarks, function(benchmarks, key){
			report[key] = {them:[]};
			report[key].total = 0;
			benchmarks.each(function(benchmark){
				benchmark.total = benchmark.end - benchmark.start;
				report[key].them.push(benchmark.total);
				report[key].total += benchmark.total;
			});
			report[key].count = report[key].them.length;
			report[key].average = report[key].total / report[key].count;
			delete report[key].them;
		});
		report_text = '';
		for (var property in report) {
			report_text += property;
			report_text += ': ';
			report_text += pp(report[property]);
			report_text += '\n';
		}
		try{
			console.log(report_text);
		}catch(e){
			alert(report_text);
		};
	}
	
});

usage.js

SubtleBenchmarker.start('Benchmark Name');
// Do something that takes a long time or something
SubtleBenchmarker.end('Benchmark Name');

SubtleBenchmarker.start('Benchmark Name');
// Do the same thing again
SubtleBenchmarker.end('Benchmark Name');

SubtleBenchmarker.start('a different Benchmark Name');
// Do something else
SubtleBenchmarker.end('a different Benchmark Name');


SubtleBenchmarker.report(); // View a report of all your activities