handler.deleteProperty()

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

target

The target object.

property

A string or Symbol representing the property name.

The deleteProperty() method must return a Boolean indicating whether or not the property has been successfully deleted. Other values are coerced to booleans.

Many operations, including the delete operator when in strict mode, throw a TypeError if the [[Delete]] internal method returns false.

This trap can intercept these operations:

• The delete operator: delete proxy[foo] and delete proxy.foo
• Reflect.deleteProperty()

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

The proxy's [[Delete]] internal method throws a TypeError if the handler definition violates one of the following invariants:

• A property cannot be reported as deleted, if it exists as a non-configurable own property of the target object. That is, if Reflect.getOwnPropertyDescriptor() returns configurable: false for the property on target, then the trap must return a falsy value.
• A property cannot be reported as deleted, if it exists as an own property of the target object and the target object is non-extensible. That is, if Reflect.isExtensible() returns false on target, and Reflect.getOwnPropertyDescriptor() returns a property descriptor for the property on target, then the trap must return a falsy value.

The following code traps the delete operator.

const p = new Proxy(
  {},
  {
    deleteProperty(target, prop) {
      if (!(prop in target)) {
        console.log(`property not found: ${prop}`);
        return false;
      }
      delete target[prop];
      console.log(`property removed: ${prop}`);
      return true;
    },
  },
);

p.a = 10;
console.log("a" in p); // true

const result1 = delete p.a; // "property removed: a"
console.log(result1); // true
console.log("a" in p); // false

const result2 = delete p.a; // "property not found: a"
console.log(result2); // false

• Proxy
• Proxy() constructor
• delete
• Reflect.deleteProperty()