test the performance of let and var

benchmark.js

// basic performance test of let and var in node v5.2.0

"use strict"
var n = Date.now();
var count = 0;
for(var i = 0; i < 10000000000; i++){
  count += i;
}
console.log(Date.now() - n);
//run 1:35443
//run 2:35779
//run 3:35415



var now = Date.now();
var ct = 0;
for(let i = 0; i < 10000000000; i++){
  count += i;
}
console.log(Date.now() - now);
//run 1:20660
//run 2:20654
//run 3:20735