The Reflect.has()
static method is like the in
operator, but as a function.
The Reflect.has()
static method is like the in
operator, but as a function.
Reflect.has(target, propertyKey)
target
The target object in which to look for the property.
propertyKey
The name of the property to check.
A Boolean
indicating whether or not the target
has the property.
TypeError
Thrown if target
is not an object.
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
.
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
Specification |
---|
ECMAScript Language Specification # sec-reflect.has |
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 |
© 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