Object Methods

This lesson explains Object Methods in JavaScript with beginner-friendly examples, practical use cases, and clear best practices.

JavaScript Object Methods Overview

JavaScript Object methods are built-in methods used to create, inspect, copy, freeze, seal, compare, group, and manage objects. They help developers work with object properties, key-value pairs, prototypes, descriptors, and object immutability in a clean and reliable way.

Object methods are commonly used in frontend applications, backend APIs, React state management, data transformation, configuration objects, and JavaScript interviews.

JavaScript Object Methods Example

const user = {
  name: "John",
  age: 30,
  role: "Developer"
};

console.log(Object.keys(user));
console.log(Object.values(user));
console.log(Object.entries(user));

const copyUser = Object.assign({}, user);

console.log(copyUser);

This example shows how to get object keys, values, entries, and create a shallow copy using common JavaScript Object methods.

Top 10 JavaScript Object Method Examples

#	Method	Syntax
1	Get Keys	`Object.keys({ name: "John", age: 30 })`
2	Get Values	`Object.values({ name: "John", age: 30 })`
3	Get Entries	`Object.entries({ name: "John" })`
4	Create From Entries	`Object.fromEntries([["name", "John"]])`
5	Copy Object	`Object.assign({}, user)`
6	Freeze Object	`Object.freeze(user)`
7	Seal Object	`Object.seal(user)`
8	Check Own Property	`Object.hasOwn(user, "name")`
9	Compare Values	`Object.is(NaN, NaN)`
10	Group Data	`Object.groupBy(users, user => user.role)`

JavaScript Object Built-in Methods with Examples and Output

Method	Description	Example	Output
`Object.keys()`	Returns object keys.	`Object.keys({ name: "John", age: 30 })`	`["name", "age"]`
`Object.values()`	Returns object values.	`Object.values({ name: "John", age: 30 })`	`["John", 30]`
`Object.entries()`	Returns key-value pairs.	`Object.entries({ name: "John" })`	`[["name", "John"]]`
`Object.fromEntries()`	Creates object from entries.	`Object.fromEntries([["name", "John"]])`	`{ name: "John" }`
`Object.assign()`	Copies properties into target object.	`Object.assign({}, { a: 1 }, { b: 2 })`	`{ a: 1, b: 2 }`
`Object.create()`	Creates object with a prototype.	`Object.create({ type: "user" })`	`New object with prototype`
`Object.freeze()`	Prevents adding, deleting, or updating properties.	`Object.freeze({ name: "John" })`	`Frozen object`
`Object.isFrozen()`	Checks if object is frozen.	`Object.isFrozen(Object.freeze({}))`	`true`
`Object.seal()`	Prevents adding or deleting properties.	`Object.seal({ name: "John" })`	`Sealed object`
`Object.isSealed()`	Checks if object is sealed.	`Object.isSealed(Object.seal({}))`	`true`
`Object.preventExtensions()`	Prevents adding new properties.	`Object.preventExtensions({ name: "John" })`	`Non-extensible object`
`Object.isExtensible()`	Checks if object can be extended.	`Object.isExtensible({})`	`true`
`Object.hasOwn()`	Checks if object has its own property.	`Object.hasOwn({ name: "John" }, "name")`	`true`
`hasOwnProperty()`	Checks if property exists directly on object.	`({ name: "John" }).hasOwnProperty("name")`	`true`
`Object.is()`	Compares two values accurately.	`Object.is(NaN, NaN)`	`true`
`Object.getPrototypeOf()`	Returns object prototype.	`Object.getPrototypeOf({})`	`Object.prototype`
`Object.setPrototypeOf()`	Sets object prototype.	`Object.setPrototypeOf(obj, proto)`	`Updated object`
`Object.defineProperty()`	Defines one property with descriptor.	`Object.defineProperty(obj, "id", { value: 1 })`	`Object with id property`
`Object.defineProperties()`	Defines multiple properties.	`Object.defineProperties(obj, { id: { value: 1 } })`	`Object with multiple properties`
`Object.getOwnPropertyDescriptor()`	Returns descriptor for one property.	`Object.getOwnPropertyDescriptor(obj, "name")`	`Descriptor object`
`Object.getOwnPropertyDescriptors()`	Returns descriptors for all properties.	`Object.getOwnPropertyDescriptors(obj)`	`Descriptors object`
`Object.getOwnPropertyNames()`	Returns own property names.	`Object.getOwnPropertyNames({ a: 1 })`	`["a"]`
`Object.getOwnPropertySymbols()`	Returns symbol properties.	`Object.getOwnPropertySymbols(obj)`	`[Symbol()]`
`Object.groupBy()`	Groups items by callback result.	`Object.groupBy(users, user => user.role)`	`{ admin: [...], user: [...] }`

Best Practices

Use Object.keys() when you need property names.
Use Object.values() when you need only values.
Use Object.entries() when looping through key-value pairs.
Use Object.assign() for shallow copying objects.
Use Object.freeze() for constants and configuration objects.
Use Object.hasOwn() instead of relying on prototype properties.

Key Takeaways

JavaScript Object methods help inspect and manage objects.
Object.keys(), Object.values(), and Object.entries() are the most commonly used methods.
Object.freeze() and Object.seal() help control object changes.
Object.assign() creates a shallow copy.
Object methods are important for APIs, React state, Node.js, and interviews.