ProxyHandler : Object

The ProxyHandler is used by %%/Proxy|Proxy%% to intercept and modify

the behavior of the proxied object. You may use any JavaScript object

as a ProxyHandler. If any of the following methods are not provided,

the Proxy will use the default behavior for that method.

Version:

ECMAScript 2015

----

instance.apply(target : Function, thisArg : Object, parameters : Array) : Object

Called when

**proxy(...)**,

%%/Function#apply|**proxy.apply(thisArg, parameters)**%%,

or

%%/Function#call|**proxy.call(thisArg, ...parameters)**%%

are called.

<example>

var x = function(arg1, arg2) {

console.log('in x(' + arg1 + ', ' + arg2 + ')');

};

var proxy = new Proxy(x, {

apply: function(target, thisArg, parameters) {

console.log('in apply');

return target.apply(thisArg, parameters);

}

});

proxy('direct1', 'direct2');

proxy.apply(null, ['apply1', 'apply2']);

proxy.call(null, 'call1', 'call2');

</example>

----

instance.construct(target : Function, parameters : Array) : Object

Called when **new target(...parameters)** is called.

<example>

var Button = function(text) {

this.text = text;

};

var ButtonProxy = new Proxy(Button, {

construct: function(target, parameters) {

console.log('in construct');

var button = Object.create(target.prototype);

target.apply(button, parameters);

return button;

}

});

var button = new ButtonProxy('OK');

console.log(button.text);

</example>

----

instance.defineProperty(target : Object, name : String, propertyDescriptor : PropertyDescriptor) : undefined

Called when %%/Object#defineProperty|**Object.defineProperty()**%%

is called on the proxy.

<example>

var x = { foo: 1 };

var proxy = new Proxy(x, {

defineProperty: function(target, name, propertyDescriptor) {

console.log('in defineProperty');

return Object.defineProperty(target, name, propertyDescriptor);

}

});

Object.defineProperty(proxy, 'bar', { value: 2,

writable: true,

enumerable: false,

configurable: true } );

</example>

----

instance.deleteProperty(target : Object, name : String) : Boolean

Called when **delete proxy[name]** is called. Return **true**

if the delete was successful.

<example>

var x = { foo: 1 };

var proxy = new Proxy(x, {

deleteProperty: function(target, name) {

console.log('in deleteProperty');

return delete target[name];

}

});

delete proxy.foo;

console.log(proxy.foo);

console.log(x.foo);

</example>

----

instance.enumerate(target : Object) : Array<String>

----

prototype.get(target : Object, name : String, proxy : Proxy) : Object

Called when reading the **name** property of the **target** of the proxy.

The return value is used as the value of the property.

<example>

var x = { foo: 1 };

var proxy = new Proxy(x, {

get: function(target, name, proxy) {

console.log('in get');

var value = target[name];

if (typeof value === 'string') {

value = value.toUpperCase();

}

return value;

}

});

console.log(proxy.foo);

console.log(x.foo); // value stored on x is unmodified

</example>

----

instance.getOwnPropertyDescriptor(target : Object, name : String) : PropertyDescriptor

Called when %%/Object#getOwnPropertyDescriptor|**Object.getOwnPropertyDescriptor()**%%

is called on the %%/Proxy|Proxy%%.

<example>

var x = { foo: 1 };

var proxy = new Proxy(x, {

getOwnPropertyDescriptor: function(target, name) {

console.log('in getOwnPropertyDescriptor');

return Object.getOwnPropertyDescriptor(target, name);

}

});

console.dir(Object.getOwnPropertyDescriptor(proxy, 'foo'));

</example>

----

instance.has(target : Object, name : String) : Boolean

Called when **name in proxy** is called.

<example>

var x = { foo: 1 };

var proxy = new Proxy(x, {

has: function(target, name) {

console.log('in has');

return name in target;

}

});

console.log('foo' in proxy);

</example>

----

prototype.isExtensible(target : Object) : Boolean

Called when checking to see if an Object is %%/Object#isExtensible|extensible%%.

<example>

var x = { foo: 1 };

var proxy = new Proxy(x, {

isExtensible: function(target) {

console.log('in isExtensible');

return Object.isExtensible(target);

}

});

console.log(Object.isExtensible(proxy));

Object.preventExtensions(proxy);

console.log(Object.isExtensible(proxy));

</example>

----

instance.ownKeys(target : Object) : Array<String>

Called when

%%/Object#keys|**Object.keys()**%%,

%%/Object#getOwnPropertyNames|**Object.getOwnPropertyNames()**%%,

or

%%/Object#getOwnPropertySymbols|**Object.getOwnPropertySymbols()**%%

are called on the proxy.

<example>

var x = { foo: 1 };

Object.defineProperty(x, 'bar', { value: 2,

writable: true,

enumerable: false,

configurable: true } );

var proxy = new Proxy(x, {

ownKeys: function(target, a, b) {

console.log('in ownKeys');

var names = Object.getOwnPropertyNames(target);

var symbols = Object.getOwnPropertySymbols(target);

return names.concat(symbols);

}

});

console.log(Object.keys(proxy));

console.log(Object.getOwnPropertyNames(proxy));

console.log(Object.getOwnPropertySymbols(proxy));

</example>

----

prototype.preventExtensions(target : Object) : Boolean

Called when %%Object#preventExtensions|**Object.preventExtensions()**%%

is called on the %%/Proxy|Proxy%%. Return **true** if

preventExtensions succeeded.

<example>

var x = { foo: 1 };

var proxy = new Proxy(x, {

preventExtensions: function(target) {

console.log('in preventExtensions');

Object.preventExtensions(target);

return !Object.isExtensible(target);

}

});

console.log(Object.isExtensible(proxy));

console.log(Object.preventExtensions(proxy));

console.log(Object.isExtensible(proxy));

</example>

----

instance.set(target : Object, name : String, value : Object, proxy : Proxy) : Object

Called when setting the **name** property of the **target** of the proxy.

<example>

var x = { foo: 1 };

var proxy = new Proxy(x, {

set: function(target, name, value, proxy) {

console.log('in set');

target[name] = value.toUpperCase();

}

});

proxy.foo = 'bar';

console.log(proxy.foo);

console.log(x.foo); // value stored on x is uppercase

</example>