Objects in JavaScript

What is an Object?

An object is a collection of key-value pairs. Unlike arrays which are ordered lists, objects are unordered collections that you access by name (the key).

Creating Objects

// Object literal (preferred)
let person = {
  name: "Alice",
  age: 25,
  city: "New York"
};

// Using the Object constructor
let car = new Object();
car.make = "Toyota";
car.model = "Camry";

Accessing Properties

Two ways: dot notation or bracket notation.

let person = { name: "Alice", age: 25 };

// Dot notation
console.log(person.name); // "Alice"

// Bracket notation (useful for dynamic keys)
console.log(person["age"]); // 25

// Adding new properties
person.city = "New York";

Object Methods

A method is a function that belongs to an object.

let person = {
  name: "Alice",
  age: 25,
  greet: function() {
    console.log("Hello, I'm " + this.name);
  }
};

person.greet(); // "Hello, I'm Alice"

The this Keyword

this refers to the object that the method belongs to. It's one of the most important concepts in JavaScript.

let person = {
  name: "Alice",
  introduce: function() {
    return "My name is " + this.name;
  }
};

console.log(person.introduce()); // "My name is Alice"

Common Mistakes

• Confusing this behavior in different contexts (we'll cover this in detail later)
• Forgetting to use new when using constructor functions
• Accidentally creating global variables when using objects

Quick Quiz

Summary

• Objects are collections of key-value pairs
• Use dot notation or bracket notation to access properties
• Methods are functions stored as properties
• this refers to the object the method belongs to
• Use Object.keys() and Object.values() to iterate