The handler.deleteProperty() method is a trap for the [[Delete]] object internal method, which is used by operations such as the delete operator.
const monster = {
texture: "scaly",
};
const handler = {
deleteProperty(target, prop) {
if (prop in target) {
delete target[prop];
console.log(`property removed: ${prop}`);
// Expected output: "property removed: texture"
}
},
};
console.log(monster.texture);
// Expected output: "scaly"
const proxy = new Proxy(monster, handler);
delete proxy.texture;
console.log(monster.texture);
// Expected output: undefinednew Proxy(target, {
deleteProperty(target, property) {
}
})The following parameters are passed to the deleteProperty() method. this is bound to the handler.
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:
delete operator: delete proxy[foo] and delete proxy.fooReflect.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:
Reflect.getOwnPropertyDescriptor() returns configurable: false for the property on target, then the trap must return a falsy value.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