Object.getOwnPropertyDescriptor()

The Object.getOwnPropertyDescriptor() method returns an object describing the configuration of a specific property on a given object (that is, one directly present on an object and not in the object's prototype chain). The object returned is mutable but mutating it has no effect on the original property's configuration.

Object.getOwnPropertyDescriptor(obj, prop)

obj

The object in which to look for the property.

prop

The name or Symbol of the property whose description is to be retrieved.

A property descriptor of the given property if it exists on the object, undefined otherwise.

This method permits examination of the precise description of a property. A property in JavaScript consists of either a string-valued name or a Symbol and a property descriptor. Further information about property descriptor types and their attributes can be found in Object.defineProperty().

A property descriptor is a record with some of the following attributes:

value

The value associated with the property (data descriptors only).

writable

true if and only if the value associated with the property may be changed (data descriptors only).

get

A function which serves as a getter for the property, or undefined if there is no getter (accessor descriptors only).

set

A function which serves as a setter for the property, or undefined if there is no setter (accessor descriptors only).

configurable

true if and only if the type of this property descriptor may be changed and if the property may be deleted from the corresponding object.

enumerable

true if and only if this property shows up during enumeration of the properties on the corresponding object.

var o, d;

o = { get foo() { return 17; } };
d = Object.getOwnPropertyDescriptor(o, 'foo');
// d is {
//   configurable: true,
//   enumerable: true,
//   get: /*the getter function*/,
//   set: undefined
// }

o = { bar: 42 };
d = Object.getOwnPropertyDescriptor(o, 'bar');
// d is {
//   configurable: true,
//   enumerable: true,
//   value: 42,
//   writable: true
// }

o = { [Symbol.for('baz')]: 73 }
d = Object.getOwnPropertyDescriptor(o, Symbol.for('baz'));
// d is {
//   configurable: true,
//   enumerable: true,
//   value: 73,
//   writable: true
// }

o = {};
Object.defineProperty(o, 'qux', {
  value: 8675309,
  writable: false,
  enumerable: false
});
d = Object.getOwnPropertyDescriptor(o, 'qux');
// d is {
//   value: 8675309,
//   writable: false,
//   enumerable: false,
//   configurable: false
// }

In ES5, if the first argument to this method is not an object (a primitive), then it will cause a TypeError. In ES2015, a non-object first argument will be coerced to an object at first.

Object.getOwnPropertyDescriptor('foo', 0);
// TypeError: "foo" is not an object  // ES5 code

Object.getOwnPropertyDescriptor('foo', 0);
// Object returned by ES2015 code: {
//   configurable: false,
//   enumerable: true,
//   value: "f",
//   writable: false
// }

• Object.defineProperty()
• Reflect.getOwnPropertyDescriptor()