Avoiding built-in object look ups.

gistfile1.js

var start = new Date().getTime();

var sum = 0;
for (i = 0; i < 5000000; ++i) {
  sum += Math.sin(Math.random());
}

var end = new Date().getTime();

var time = end - start;
console.info('Builtin object lookup: execution time: ' + time, sum);

sin = Math.sin;

var start = new Date().getTime();

var sum = 0;
for (i = 0; i < 5000000; ++i) {
  sum += sin(Math.random());
}

var end = new Date().getTime();
var time = end - start;
console.info('Local variable: execution time: ' + time, sum);