MiniJSperf

A JSperf clone golfed by xem, p01, Subzey and Aemkei, in 250b

<body onload='for(i in v="value")f.innerHTML+="<textarea id=_"+
i+">//"+["before",1,2,"after","result"][i]'id=f><button onclick
='for($=0;$<2;eval(Array(1e5).join(_0[v]+(n="\n")+($++?_2:_1)[v
]+n+_3[v]+n)),_4[v]+=n+$+":"+(new Date-_)+"ms")_=new Date'>Go

Try / download

Demo

PS: ~~ is faster than Math.floor