Inspect inheritance
Check whether an object inherits from a particular prototype.
JavaScript · Function
Object.getPrototypeOf
Object.getPrototypeOf() returns the internal [[Prototype]] of a value. Its result is an object or null; modern JavaScript coerces primitive arguments to wrapper objects before retrieving the prototype.
How it works
Object.getPrototypeOf(obj) retrieves obj's internal [[Prototype]] value. The result is either an object or null; in current JavaScript, a primitive argument is converted to its corresponding wrapper object before the prototype is read.
Syntax
Object.getPrototypeOf(obj)Parameters
| Name | Type | Description |
|---|---|---|
obj | Object | The value whose prototype is returned. |
Returns
The prototype of the supplied value, which may be null.
Key points
- It is a static Object method that returns the specified object's prototype.
- The returned value corresponds to the object's internal [[Prototype]].
- Its only parameter is the value whose prototype should be inspected.
- The result can be an object or null.
- Call the function with one argument: Object.getPrototypeOf(obj).
- It can verify that an object was created with a particular prototype.
Common mistakes
- Primitive arguments are coerced to objects in ES2015+, so Object.getPrototypeOf("foo") returns String.prototype rather than throwing.
- Handle null as a valid result, especially when inspecting Object.prototype or objects created with a null prototype.
Example: Read an object's prototype
const prototype = { greet() { return "hello"; } };
const object = Object.create(prototype);
console.log(Object.getPrototypeOf(object) === prototype); // true
console.log(Object.getPrototypeOf(Object.prototype)); // nullCreates an object with a chosen prototype, then retrieves that prototype and confirms the end of the standard object chain.
When to use it
Traverse the prototype chain
Walk an object's prototype chain until the result is null.
Validate object construction
Verify the prototype assigned by Object.create() or a constructor.
Related
Object.create()Object.setPrototypeOf()Reflect.getPrototypeOf()Object.prototype.__proto__