Basics

Objects

Key-value collections — the building block of JS.

1. Explanation

Objects store related data as key-value pairs. Access values with dot or bracket notation. Use Object.keys / values / entries to iterate. Spread (...) clones or merges objects. Destructuring pulls properties into variables.

2. Example

Try it yourself

const user = {
  name: "Aman",
  age: 22,
  skills: ["html", "css", "js"],
};

console.log(user.name);           // Aman
console.log(user["age"]);         // 22

const { name, age } = user;       // destructuring
const updated = { ...user, age: 23 }; // spread + override

console.log(name, age);
console.log(updated);

Console

Click Run to see output.

3. Expected output

output

Aman
22
Aman 22
{"name":"Aman","age":23,"skills":["html","css","js"]}

4. Common mistakes

✗Using = to 'copy' an object — you only copy the reference, not the data
✗Forgetting that Object.keys returns strings only, not symbols
✗Trying to JSON.stringify an object with circular references

5. Practice questions

Create a 'book' object with title, author, year and log each property
Use destructuring to extract two properties at once
Merge two objects using the spread operator

→ Try more practice problems