JS: Dots are bad, M'kay?

• When the return value of a function is needed multiple times, and the value is a constant, a variable should be used to cache it.
• In JavaScript, every dot that appears in a statement is equivalent to a function call.

• Run the following code and you should see a 20% to 50% performance increase, depending on the browser, when you avoid the dots.

var limit = 1000000;

var bigArray = new Array(limit);

// array.length

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

for (var i = 0; i < bigArray.length; i++) {

   var x = Math.random();

}

document.write("array.length: " + ((new Date()).getTime() - start) + "<br/>");

// len = array.length

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

for (var i = 0, len = bigArray.length; i < len; i++) {

   var x= Math.random();

}

document.write("len: " + ((new Date()).getTime() - start) + "<br/>");

//Math.floor

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

for (var i = 0; i < limit; i++) {

   var x = Math.floor(Math.random());

}

document.write("Math.floor: " + ((new Date()).getTime() - start) + "<br/>");

// | 0

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

for (var i = 0; i < limit; i++) {

   var x = Math.random() | 0; // floor.

}

document.write("| 0: " + ((new Date()).getTime() - start) + "<br/>");