JavaScript Object Mirroring/One-way Property Syncing

Question

For security purposes, I have a need for a \"mirrored\" object. i.e. if I create object A, and shallow-clone a copy of A and call it B, whenever a property of A changes, I hope

Answer 1

You can setup the prototype chain for this:

var a = {};
var Syncer = function(){};
Syncer.prototype = a;
var b = new Syncer();

a.foo = 123;
b.foo; // 123

b.bar = 456;
a.bar // undefined

Any property not set on b directly will be looked for on the prototype object, which is a.

You can even wrap this up in a convenience function:

var follow = function(source) {
  var Follower = function(){};
  Follower.prototype = source;
  return new Follower();
}

var a = {};
var b = follow(a);

a.foo = 123;
b.bar = 456;

a.foo; // 123
b.foo; // 123

a.bar; // undefined
b.bar; // 456