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
targetis 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® 2027 Language Specification # sec-reflect.has |
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Legend
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