Reflect.has()

const object = {
  property1: 42,
};

console.log(Reflect.has(object, "property1"));
// : true

console.log(Reflect.has(object, "property2"));
// : false

console.log(Reflect.has(object, "toString"));
// : true

Reflect.has(target, propertyKey)

propertyKey in target;

Reflect.has({ x: 0 }, "x"); // true
Reflect.has({ x: 0 }, "y"); // false

// true 
Reflect.has({ x: 0 }, "toString");

// Proxy with .has() handler method
obj = new Proxy(
  {},
  {
    has(t, k) {
      return k.startsWith("door");
    },
  },
);
Reflect.has(obj, "doorbell"); // true
Reflect.has(obj, "dormitory"); // false

const a = { foo: 123 };
const b = { __proto__: a };
const c = { __proto__: b };
// The prototype chain is: c -> b -> a
Reflect.has(c, "foo"); // true