Reflect : Object

Provides methods to inspect and interact with objects programmatically. Similar

to pre-ECMAScript 2015 methods on %%/Object|Object%% and %%/Function|Function%%.

Version:

ECMAScript 2015

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect-object

----

apply(target : Object, thisArg : Object, parameters : Array) : Object

See %%/Function#apply|Function.apply()%%.

<example>

var whatsThis = function() { console.log(this); }

Reflect.apply(whatsThis, 'hello', []);

// Call a function that takes a variable number of args

var numbers = [3, 20, 1, 45];

console.log(Reflect.apply(Math.max, undefined, numbers));

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.apply

----

construct(constructor : Function, parameters : Array, [newTarget : Function]) : Object

Essentially the same as **new constructor(...parameters)**. **newTarget** allows

you to change what the **new.target** value is inside the constructor.

<example>

class MyClass {

constructor(...args) {

console.log('constructing MyClass', ...args);

}

}

// The following are equivalent:

var a = new MyClass(1, 2, 3);

var b = Reflect.construct(MyClass, [1, 2, 3]);

console.log();

class WithTarget {

constructor() {

console.log('constructing WithTarget. new.target=' + new.target.name);

}

}

var c = new WithTarget();

var d = Reflect.construct(WithTarget, []);

var e = Reflect.construct(WithTarget, [], MyClass);

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.construct

----

defineProperty(obj : Object, propertyName : String, propertyDescriptor : PropertyDescriptor) : Boolean

The same as %%/Object#defineProperty|Object.defineProperty()%% except returns

**false** on failure instead of throwing an exception.

<example>

var x = { };

var fooDescriptor = { value: 1,

writable: true,

enumerable: false,

configurable: true } ;

var barDescriptor = { value: 2,

writable: true,

enumerable: false,

configurable: true } ;

console.log(Reflect.defineProperty(x, 'foo', fooDescriptor));

Object.defineProperty(x, 'bar', barDescriptor);

console.log(x.foo);

console.log(x.bar);

console.log();

var y = { foo: 1 };

Object.seal(y);

console.log(Reflect.defineProperty(y, 'foo', fooDescriptor));

try {

Object.defineProperty(y, 'bar', barDescriptor);

}

catch(e) {

console.log(e);

}

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.defineProperty

----

deleteProperty(obj : Object, propertyName : String) : Boolean

The same as **delete object[propertyName]**. Returns **true** if the value

was deleted (ie, the property was configurable).

<example>

var x = { foo: 1, bar: 2 };

// The following are equivalent:

console.log(delete x.foo);

console.log(delete x['foo']);

console.log(Reflect.deleteProperty(x, 'foo'));

console.log('x.foo=' + x.foo);

console.log();

Object.seal(x);

console.log(delete x.bar);

console.log(delete x['bar']);

console.log(Reflect.deleteProperty(x, 'bar'));

console.log('x.bar=' + x.bar);

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.defineProperty

----

get(target : Object, propertyName : String, [getterThis : Object]) : Object

The same as **target[propertyName]**. If **propertyName** is a get function,

**target** is used as its **this** if **getterThis** is not specified.

<example>

var x = { foo: 1 };

// The following are equivalent:

console.log(x.foo);

console.log(x['foo']);

console.log(Reflect.get(x, 'foo'));

console.log();

// Example of getter functions:

x = { bar: 2, get baz() { return this.bar; } };

console.log(x.baz);

console.log(x['baz']);

console.log(Reflect.get(x, 'baz'));

console.log(Reflect.get(x, 'baz', { bar: 3 }));

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.get

----

getOwnPropertyDescriptor(obj : Object, propertyName : String) : PropertyDescriptor

The same as %%/Object#getOwnPropertyDescriptor|Object.getOwnPropertyDescriptor()%%

except throws an exception if **obj** is not an Object.

<example>

var x = { foo: 1 };

// The following are equivalent:

console.dir(Reflect.getOwnPropertyDescriptor(x, 'foo'));

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

// Reflect throws an exception if the parameter is not an Object

try {

console.log(Reflect.getPrototypeOf(1, 'foo'));

}

catch(e) {

console.log(e);

}

console.log(Object.getOwnPropertyDescriptor(1, 'foo'));

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.getownpropertydescriptor

----

getPrototypeOf(obj : Object) : Object

The same as %%/Object#getPrototypeOf|Object.getPrototypeOf()%% except throws

an exception if **obj** is not an Object.

<example>

console.log(Reflect.getPrototypeOf([]) === Array.prototype);

console.log(Object.getPrototypeOf([]) === Array.prototype);

// Reflect throws an exception if the parameter is not an Object

try {

console.log(Reflect.getPrototypeOf(1));

}

catch(e) {

console.log(e);

}

console.log(Object.getPrototypeOf(1));

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.getprototypeof

----

has(obj : Object, propertyName : String) : Boolean

Returns **true** if **obj** has a property named **propertyName**. The **in**

operator provides the same result.

<example>

var x = { foo: 1 };

console.log(Reflect.has(x, 'foo'));

console.log('foo' in x);

console.log(Reflect.has(x, 'bar'));

console.log('bar' in x);

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.has

----

isExtensible(obj : Object) : Boolean

The same as %%/Object#isExtensible|Object.isExtensible()%% except throws

an exception if **obj** is not an Object.

<example>

var x = { foo: 1 };

console.log(Reflect.isExtensible(x));

Reflect.preventExtensions(x);

console.log(Reflect.isExtensible(x));

// Reflect throws an exception if the parameter is not an Object

try {

console.log(Reflect.isExtensible(1));

}

catch (e) {

console.log(e);

}

console.log(Object.isExtensible(1));

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.isextensible

----

ownKeys(obj : Object) : Array<String>

The same as %%/Object#getOwnPropertyNames|Object.getOwnPropertyNames()%% except

throws an exception if **obj** is not an Object.

<example>

var x = { foo: 1, bar: 2 };

console.log(Reflect.ownKeys(x));

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

// Reflect throws an exception if the parameter is not an Object

try {

console.log(Reflect.ownKeys(1));

}

catch (e) {

console.log(e);

}

console.log(Object.getOwnPropertyNames(1));

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.ownkeys

----

preventExtensions(obj : Object) : Boolean

The same as %%/Object#preventExtensions|Object.preventExtensions()%% except

returns **false** on failure and throws an exception if **obj** is not an Object.

<example>

var x = { foo: 1 };

// The following are equivalent

console.log(Reflect.preventExtensions(x));

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

x.bar = 2;

console.log(x);

// Reflect throws an exception if the parameter is not an Object

try {

console.log(Reflect.preventExtensions(1));

}

catch (e) {

console.log(e);

}

console.log(Object.preventExtensions(1));

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.preventextensions

----

set(target : Object, propertyName : String, value : Object, [setterThis : Object]) : Boolean

The same as **target[propertyName] = value**. Returns **true** if the set was

successful and **false** otherwise (if the object was %%Object#freeze|frozen%% for

example). If **propertyName** is a set

function, **target** is used as its **this** if **setterThis** is not specified.

<example>

var x = { foo: 1 };

// The following are equivalent:

x.bar = 2;

x['bar'] = 2;

console.log(Reflect.set(x, 'bar', 2));

// set returns false if the object is frozen

Object.freeze(x);

console.log(Reflect.set(x, 'bar', 2));

// Example of setter functions and setterThis arg:

x = { bar: 2,

set baz(value) {

console.log(`baz=${value} where this.bar = ${this.bar}; `);

}

};

x.baz = 42;

x['baz'] = 42;

Reflect.set(x, 'baz', 42);

Reflect.set(x, 'baz', 42, { bar: 3 });

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.set

----

setPrototypeOf(obj : Object, proto : Object) : Boolean

Changes the %%/Function#prototype|prototype%% of **obj** to **proto**.

<example>

var Button = function(content) {

this.content = content;

};

Button.prototype.click = function() {

console.log(this.content + ' clicked');

}

// Instead of 'new Button()', the following changes

// the prototype of a regular object to be Button's

// prototype after the object has been created.

var myButton = { content: 'promoted' };

console.log(Reflect.getPrototypeOf(myButton) === Object.prototype);

Reflect.setPrototypeOf(myButton, Button.prototype);

console.log(Reflect.getPrototypeOf(myButton) === Button.prototype);

myButton.click();

</example>

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-reflect.setprototypeof