handler.defineProperty()

The handler.defineProperty() method is a trap for Object.defineProperty().

Syntax

new Proxy(target, {
  defineProperty(target, property, descriptor) {
  }
});

Parameters

The following parameters are passed to the defineProperty() method. this is bound to the handler.

• target
  • : The target object.
• property
  • : The name or Symbol of the property whose description is to be retrieved.
• descriptor
  • : The descriptor for the property being defined or modified.

Return value

The defineProperty() method must return a Boolean indicating whether or not the property has been successfully defined.

Description

The handler.defineProperty() method is a trap for Object.defineProperty().

Interceptions

This trap can intercept these operations:

• Object.defineProperty(), Object.defineProperties()
• Reflect.defineProperty()

Or any other operation that invokes the [[DefineOwnProperty]] internal method.

Invariants

If the following invariants are violated, the trap throws a TypeError when invoked.

• A property cannot be added, if the target object is not extensible.
• A property cannot be added as or modified to be non-configurable, if it does not exists as a non-configurable own property of the target object.
• A property may not be non-configurable, if a corresponding configurable property of the target object exists.
• If a property has a corresponding target object property then Object.defineProperty(target, prop, descriptor) will not throw an exception.
• In strict mode, a false return value from the defineProperty() handler will throw a TypeError exception.