Reflect.has()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2016.

The Reflect.has() static method is like the in operator, but as a function.

Try it

const object = {
  property1: 42,
};

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

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

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

Syntax

Reflect.has(target, propertyKey)

Parameters

target

The target object in which to look for the property.

propertyKey

The name of the property to check.

Return value

A Boolean indicating whether or not the target has the property.

Exceptions

TypeError

Thrown if target is not an object.

Description

Reflect.has() provides the reflective semantic of checking if a property is in an object. That is, Reflect.has(target, propertyKey) is semantically equivalent to:

propertyKey in target;

Reflect.has() invokes the [[HasProperty]] object internal method of target.

Examples

Using Reflect.has()

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

// returns true for properties in the prototype chain
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

Reflect.has returns true for any inherited properties, like the in operator:

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