Reflect.has()
The Reflect.has()
static method is like the in
operator, but
as a function.
Try it
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
Specification |
---|
ECMAScript Language Specification # sec-reflect.has |
Browser compatibility
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