Reflect - JavaScript 编辑

Reflect is a built-in object that provides methods for interceptable JavaScript operations. The methods are the same as those of proxy handlers. Reflect is not a function object, so it's not constructible.

Description

Unlike most global objects, Reflect is not a constructor. You cannot use it with a new operator or invoke the Reflect object as a function. All properties and methods of Reflect are static (just like the Math object).

The Reflect object provides the following static functions which have the same names as the proxy handler methods.

Some of these methods are also the same as corresponding methods on Object, although they do have some subtle differences between them.

Static methods

Reflect.apply(target, thisArgument, argumentsList)

Calls a target function with arguments as specified by the argumentsList parameter. See also Function.prototype.apply().

Reflect.construct(target, argumentsList[, newTarget])

The new operator as a function. Equivalent to calling new target(...argumentsList). Also provides the option to specify a different prototype.

Reflect.defineProperty(target, propertyKey, attributes)

Similar to Object.defineProperty(). Returns a Boolean that is true if the property was successfully defined.

Reflect.deleteProperty(target, propertyKey)

The delete operator as a function. Equivalent to calling delete target[propertyKey].

Reflect.get(target, propertyKey[, receiver])

Returns the value of the property. Works like getting a property from an object (target[propertyKey]) as a function.

Reflect.getOwnPropertyDescriptor(target, propertyKey)

Similar to Object.getOwnPropertyDescriptor(). Returns a property descriptor of the given property if it exists on the object,  undefined otherwise.

Reflect.getPrototypeOf(target)

Same as Object.getPrototypeOf().

Reflect.has(target, propertyKey)

Returns a Boolean indicating whether the target has the property. Either as own or inherited. Works like the in operator as a function.

Reflect.isExtensible(target)

Same as Object.isExtensible(). Returns a Boolean that is true if the target is extensible.

Reflect.ownKeys(target)

Returns an array of the target object's own (not inherited) property keys.

Reflect.preventExtensions(target)

Similar to Object.preventExtensions(). Returns a Boolean that is true if the update was successful.

Reflect.set(target, propertyKey, value[, receiver])

A function that assigns values to properties. Returns a Boolean that is true if the update was successful.

Reflect.setPrototypeOf(target, prototype)

A function that sets the prototype of an object. Returns a Boolean that is true if the update was successful.

Examples

Detecting whether an object contains certain properties

const duck = {
  name: 'Maurice',
  color: 'white',
  greeting: function() {
    console.log(`Quaaaack! My name is ${this.name}`);
  }
}

Reflect.has(duck, 'color');
// true
Reflect.has(duck, 'haircut');
// false

Returning the object's own keys

Reflect.ownKeys(duck);
// [ "name", "color", "greeting" ]

Adding a new property to the object

Reflect.set(duck, 'eyes', 'black');
// returns "true" if successful
// "duck" now contains the property "eyes: 'black'"

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• The Proxy global object.
• The handler object.