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Reflect.has()

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

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Syntax

js
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:

js
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

Specifications

Browser compatibility

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

See also

© 2005–2023 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Reflect/has