JS 8

Excellent. After this chapter, you'll know almost everything you need for working with text in real applications.

You'll use these methods in:

• 🔍 Search bars

• 🔐 Login forms

• 📧 Email validation

• 📝 Form inputs

• 🤖 Chat apps

• 📄 Text processing

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Chapter 8 — Strings

🎯 Goal (1 line)

Learn how to manipulate text using the string methods you'll use most often in real projects.

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Think Like a Programmer

A string is simply text.

const name = "Pramod";

JavaScript gives us many built-in tools for working with text.

We'll focus only on the ones you'll use frequently.

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1. .length

Finds the number of characters.

const name = "Alice";

console.log(name.length);

Output:

5

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2. .toUpperCase()

Converts text to uppercase.

const name = "alice";

console.log(name.toUpperCase());

Output:

ALICE

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3. .toLowerCase()

const email = "ADMIN@GMAIL.COM";

console.log(email.toLowerCase());

Output:

admin@gmail.com

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4. .includes()

Checks if some text exists.

const message = "Hello JavaScript";

console.log(message.includes("Java"));

Output

true

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5. .slice()

Cuts part of a string.

const word = "JavaScript";

console.log(word.slice(0, 4));

Output

Java

Think:

JavaScript
0123456789

Starts at index 0 and stops before index 4.

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6. .trim()

Removes spaces from the beginning and end.

const username = "   Alice   ";

console.log(username.trim());

Output

Alice

Very common in login forms.

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7. .replace()

Replace text.

const sentence = "I like cats";

console.log(sentence.replace("cats", "dogs"));

Output

I like dogs

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8. .split()

Splits text into an array.

const fruits = "Apple,Banana,Orange";

console.log(fruits.split(","));

Output

["Apple", "Banana", "Orange"]

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MCQs

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Q1

What is the length?

const name = "Alice";

console.log(name.length);

A. 4

B. 5

C. 6

D. Error

✅ Answer

B

---

Q2

Output?

const city = "delhi";

console.log(city.toUpperCase());

A.

delhi

B.

DELHI

C.

Delhi

D. Error

✅ Answer

B

---

Q3

Output?

const city = "DELHI";

console.log(city.toLowerCase());

A.

DELHI

B.

Delhi

C.

delhi

D. Error

✅ Answer

C

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Q4

Output?

const text = "JavaScript";

console.log(text.includes("Java"));

A. true

B. false

C. Java

D. Error

✅ Answer

A

---

Q5

Output?

const text = "JavaScript";

console.log(text.includes("Python"));

A. true

B. false

C. undefined

D. Error

✅ Answer

B

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Q6

Output?

const word = "JavaScript";

console.log(word.slice(4));

A.

Java

B.

Script

C.

JavaScript

D. Error

✅ Answer

B

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Q7

Output?

const word = "React";

console.log(word.slice(0, 2));

A.

Re

B.

ea

C.

React

D. Error

✅ Answer

A

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Q8

Output?

const name = "   Bob   ";

console.log(name.trim());

A.

"   Bob   "

B.

Bob

C.

BOB

D. Error

✅ Answer

B

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Q9

Output?

const text = "I like tea";

console.log(text.replace("tea", "coffee"));

A.

I like tea

B.

I like coffee

C.

coffee

D. Error

✅ Answer

B

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Q10

Output?

const fruits = "Apple,Banana";

console.log(fruits.split(","));

A.

Apple Banana

B.

["Apple", "Banana"]

C.

Apple,Banana

D. Error

✅ Answer

B

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Q11

Which method checks whether text exists?

A. replace()

B. includes()

C. split()

D. trim()

✅ Answer

B

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Q12

Output?

const email = "ADMIN@gmail.com";

console.log(email.toLowerCase());

A.

ADMIN@gmail.com

B.

admin@gmail.com

C.

Admin@gmail.com

D. Error

✅ Answer

B

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Q13

Output?

const text = "JavaScript";

console.log(text.slice(0, 10));

A.

JavaScript

B.

Java

C.

Script

D. Error

✅ Answer

A

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Q14

Output?

const text = "Frontend";

console.log(text.includes("end"));

A. true

B. false

C. end

D. Error

✅ Answer

A

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Q15 (Hardest)

Predict the output.

const email = "   ADMIN@GMAIL.COM   ";

const cleaned = email
  .trim()
  .toLowerCase();

console.log(cleaned);

A.

ADMIN@GMAIL.COM

B.

admin@gmail.com

C.

   admin@gmail.com

D. Error

✅ Answer

B

Step by step:

1. trim() removes spaces.

2. toLowerCase() converts all letters to lowercase.

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Mini Coding Challenge

const sentence = "JavaScript is awesome";

console.log(sentence.includes("awesome"));
console.log(sentence.toUpperCase());

✅ Solution

Output:

true
JAVASCRIPT IS AWESOME

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Mini Project — Email Cleaner

const email = "   USER@GMAIL.COM   ";

const cleanedEmail = email
  .trim()
  .toLowerCase();

console.log(cleanedEmail);

✅ Output

user@gmail.com

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🚨 Common Beginner Mistakes

❌ Forgetting that strings are immutable

This doesn't change the original string:

const name = "alice";

name.toUpperCase();

console.log(name);

Output:

alice

Why?

Because toUpperCase() returns a new string.

Correct:

const name = "alice";

const upper = name.toUpperCase();

console.log(upper);

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❌ Forgetting trim() before validation

Wrong:

const username = "   alice   ";

if (username === "alice") {
  // won't run
}

Correct:

const username = "   alice   ";

if (username.trim() === "alice") {
  // works
}

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🧠 The 80/20 Cheat Sheet

text.length

text.toUpperCase()

text.toLowerCase()

text.includes("abc")

text.slice(0, 5)

text.trim()

text.replace("old", "new")

text.split(",")

These eight methods are the ones you'll use most often in real-world JavaScript.

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🏆 You're About 35–40% Through the Core JavaScript

Here's what you've mastered so far:

• ✅ Variables (let, const)

• ✅ Conditions (if, else)

• ✅ Functions

• ✅ Arrays

• ✅ Objects

• ✅ Loops

• ✅ Array methods (map, filter, find, some, every)

• ✅ String methods

That's a very solid foundation.

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📌 Next Chapter (Very Important)

Chapter 9 — Scope

You'll learn:

• Block scope

• Function scope

• Why const and let behave differently

• Common bugs caused by scope

• Shadowing variables

Understanding scope is essential because it's one of the most common sources of bugs in JavaScript and a frequent interview topic.