W3cubDocs

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()

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:

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

Specifications

Specification
ECMAScript® 2026 Language Specification> # sec-reflect.has>

Browser compatibility

	Desktop					Mobile							Server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	WebView on iOS	Bun	Deno	Node.js
`has`	49	12	42	36	10	49	42	36	10	5.0	49	10	1.0.0	1.0	6.0.0