A load of JavaScript things that can be done slowly or quickly.

javascript-performance.js

// == parseInt();
var width = parseInt("12.5"); // Slow

var width = ~~(1 * "12.5"); // Fast 1 * "12.5" turns string to float, ~~ double bit operator floors float to int. Chrome this is slower.

// == new Array();
var arr = new Array(); // Slow
var obj = new Object(); // Slow

var arr = []; // Fast
var obj = {}; // Fast

// == with
with (obj) { // Slow
   console.log(p);
}

var i = 10;
while (i--) console.log(obj[i].p); // Fast

// == try/catch
try { // Very slow, last resort only.
  console.log('I am slow');
} catch(e) {}

/**
 * Sources
 *
 * 1. http://net.tutsplus.com/tutorials/javascript-ajax/extreme-javascript-performance/
 *
 */