Memoizing Example for "Avoiding the Quirks"

memoize.js

// Examples based on those given in
// "Avoiding The Quirks: Lessons From A JavaScript Code Review"
// by Addy Osmani
// http://addyosmani.com/blog/lessons-from-a-javascript-code-review/


// Branching at runtime with memoization
// (wordy version)
var utils = {  
  getXHR: function() {
    if( !this.memoized || typeof this.memoized !== 'function' ) {
      if(window.XMLHttpRequest) {
        this.memoized = function() { return new XMLHttpRequest(); };
      } else if(window.ActiveXObject) {
        /*this has been simplified for example sakes*/
        this.memozied = function() { return new ActiveXObject('Microsoft.XMLHTTP'); };
      }
    }
    return this.memoized();
  }
};


// Subtler (and more efficient) version
var utils = {  
  getXHR: function() {
    if(window.XMLHttpRequest) {
      utils.getXHR = function() {
        return new XMLHttpRequest;
      }
    } else if(window.ActiveXObject) {
      utils.getXHR = function(){
        /*this has been simplified for example sakes*/
        return new ActiveXObject('Microsoft.XMLHTTP');  
      }
    }
    return utils.getXHR();
  }
};