Object Before / After differ.

gistfile1.js

var Differ = function(obj){
  this.obj = obj;
};

Differ.prototype.cacheVars = function(){
  this.cache = {};
  for(var prop in this.obj){
    this.cache[prop] = this.obj[prop];
  }
};

Differ.prototype.diff = function(){
  for(var prop in this.obj){
    // it is the same
    if(this.obj[prop] === this.cache[prop]){
      continue;
    }
    else{
      // it has changed
      if(this.cache[prop] && this.obj[prop] !== this.cache[prop]){
        console.log(prop+' changed from: '+this.cache[prop]+' to: '+this.obj[prop] + '!');
      }
      else{
        // it is new
        if(this.obj[prop] && !this.cache[prop]){
          console.log(prop+' was introduced! Value is: '+this.obj[prop]);
        }
      }
    }
  }
  // check for deleted properties
  for(var prop in this.cache){
    // it was deleted
    if(this.cache[prop] !== undefined && this.obj[prop] === undefined){
      console.log(prop+' was deleted!');
    }
  }
};

// Use like:
//
var myDiffer = new Differ(window);

window.foo = 'bar'
window.bar = 'baz'

myDiffer.cacheVars();

window.qux = 1;
window.foo = function(){console.log('baz')};
delete window.bar;

myDiffer.diff();

use obj instead of thing, replaced a few missing window / obj references,

wish i could come up with a better short name for what this thing does.

Delta? I think I prefer Differ/diff.