JSFiddle - React, Tailwind, and code Playground

JavaScript

var timer = function(name) {
    var start = new Date();
    return {
        stop: function() {
            var end  = new Date();
            var time = end.getTime() - start.getTime();
            console.log('Timer:', name, 'finished in', time, 'ms');
        }
    }
};

function repeat(s,n) { return Array(n+1).join(s); }

var t = timer('Benchmark'); // <-- START BENCHMARK
for(var i = 0; i < 100000; i++)
repeat("boo", 40);
t.stop();  // <-- STOP BENCHMARK