Question

It’s recommended to cache globals locally for better performance like so:

function showWindowSize() {
    var w = window;
    var width = w.innerWidth;
    var height = w.innerHeight;
    alert("width: " + width + " height: " + height);
}

Is the same true when using the “this” keyword, or is it cached already?

Example:

Game.prototype.runGameLoop = function() {
  var self = this;
  self.update();
  self.draw();
};

Answer 1

The symbol this is always a local reference, so there’s no need to “cache” it for performance reasons. There may be other reasons to preserve its value in another local variable however. When there’s a local function that needs access to the this value from its containing function, then the containing function must make a copy of the value, since this is always set upon any function invocation.

(It may not be purely accurate to call this a “local reference”; the point is that the keyword always references a value pertinent to the local function activation record.)