Proxy : Object

The Proxy allows you to wrap an Object (called the **target**) and 
modify the behavior of that Object. 

Version:
ECMAScript 2015

Spec:
http://www.ecma-international.org/ecma-262/6.0/#sec-proxy-objects

----
new Proxy(target : Object, handler : ProxyHandler) : Proxy

Creates a new Proxy for the **target** where **handler**
allows you to modify the behavior of **target**.

<example>
// Create a Proxy for Map that only allows even number keys 
var evenMap = new Proxy(new Map(), {
  // The 'get' function allows you to modify the value returned
  // when accessing properties on the proxy
  get: function(target, name) {
    // Return a custom function for Map.set that checks
    // that the keys are even numbers
    if (name === 'set') {
      return function(key, value) {
        if (Number.isInteger(key) && (key % 2 === 0)) {
          return target.set(key, value);
        }
        else {
          throw Error('key "' + key + '" is not even');
        }
      };
    }
    else {
      // Return the normal property value for everything else
      return target[name];
    }
  }
});

evenMap.set(0, 'foo');
console.log(evenMap.get(0));

evenMap.set(2, 'bar');
console.log(evenMap.get(2));

try
{
  evenMap.set(3, 'baz');
  console.log(evenMap.get(3));
}
catch (e)
{
  console.log(e);
}
</example>

Spec:
http://www.ecma-international.org/ecma-262/6.0/#sec-proxy-target-handler

----
revocable(target : Object, handler : Proxyhandler) : Proxy

Spec:
http://www.ecma-international.org/ecma-262/6.0/#sec-proxy.revocable