Object methods
- Node.js course
- Beginner
- Lesson 68/116
- 5 min
Learn to define methods inside an object.
Object methods
When a property of an object is a function, it is called a method. In an object literal you can define methods with the shorthand: { greet() { return 'merhaba'; } }. This is the same as greet: function () { ... }.
Inside a method, the this keyword refers to the object itself. This lets you reach other properties with this.name. Example: const user = { name: 'Ayşe', greet() { return 'Merhaba ' + this.name; } }.
Call the method with a dot: user.greet(). Without parentheses you only get the function itself; to run it you need the parentheses.
Object.keys, values, entries
JavaScript provides three helpers to list an object's properties: Object.keys, Object.values and Object.entries. They live on the Object built-in, not on the object itself.
Object.keys(user) returns the property names as an array. Object.values(user) returns the values. Object.entries(user) returns an array of [name, value] pairs.
Example: Object.keys({ a: 1, b: 2 }) returns ['a', 'b']. These helpers are useful for loops and lookups.
Practice Calculator object
Define an object named calc. Its value property is 10. Its double() method returns this.value * 2. Call the method and print the result with console.log.
Starter code
// Define calc, call double() and print the resultSample solution
const calc = { value: 10, double() { return this.value * 2; } };
console.log(calc.double());Expected output
20
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does this refer to inside a method?
- The global object
- The function itself
- A new object
- The object the method belongs to Correct answer
Explanation: this refers to the object the method was called on.
2 Reach with this
const user = { name: 'Ayşe', greet() { return 'Merhaba ' + this.____; } };const user = { name: 'Ayşe', greet() { return 'Merhaba ' + this.name; } };Explanation: this.name reads the name property of user.
3 Match the Object helpers
| Term | Meaning |
|---|---|
Object.keys(o) |
Names array |
Object.values(o) |
Values array |
Object.entries(o) |
Name-value pairs |
o.method() |
Method call |