JavaScript Strings

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What is a String?

A string in JavaScript is a sequence of characters used to represent text.

const message = "Hello, world!";
const name = 'John Doe';

Strings can be written using:

• Double quotes " "
• Single quotes ' '
• Backticks (Template literals) ` `

Declaring Strings

let greeting = "Good morning";
let city = 'Mumbai';
let message = `Welcome, user!`;

String Length

const msg = "Hello";
console.log(msg.length); // 5

Accessing Characters

You can access characters using index (starting from 0):

const word = "JavaScript";
console.log(word[0]);  // J
console.log(word.charAt(4)); // S

Changing Case

const text = "Learn JavaScript";

console.log(text.toUpperCase()); // LEARN JAVASCRIPT
console.log(text.toLowerCase()); // learn javascript

Common String Methods

Method	Description	Example
length	Returns length	str.length
toUpperCase()	Converts to uppercase	"hello".toUpperCase() → "HELLO"
toLowerCase()	Converts to lowercase	"HELLO".toLowerCase() → "hello"
includes()	Checks if string contains text	"abc".includes("b") → true
indexOf()	Finds position of first occurrence	"banana".indexOf("a") → 1
lastIndexOf()	Finds position of last occurrence	"banana".lastIndexOf("a") → 5
startsWith()	Checks if string starts with given text	"hello".startsWith("he") → true
endsWith()	Checks if string ends with given text	"hello".endsWith("o") → true
slice(start, end)	Extracts part of string	"abcdef".slice(1, 4) → "bcd"
substring()	Similar to slice	"hello".substring(0, 2) → "he"
replace()	Replaces first match	"I love cats".replace("cats", "dogs")
trim()	Removes whitespace	" hello ".trim() → "hello"
split()	Splits string into array	"a,b,c".split(",") → ["a", "b", "c"]
concat()	Joins two strings	"Hi".concat(" there") → "Hi there"

Template Literals (ES6)

Template literals use backticks (` `) to support:

• Multi-line strings
• Variable interpolation using ${}

const name = "Amit";
const greeting = `Hello, ${name}!`;
console.log(greeting); // Hello, Amit!

const fullMessage = `
Dear Student,
Your result is ready.
                                    
Regards,
Admin
`;
console.log(fullMessage);

Escape Characters

Use \ (backslash) to escape special characters:

const quote = "He said, \"Let's go!\"";

Other escape sequences:

• \n - New line
• \t - Tab
• \\ - Backslash</p>

String Comparison

Strings can be compared alphabetically using ==, ===, <, >:

console.log("apple" < "banana"); // true
console.log("A" < "a"); // true (uppercase comes before lowercase)

String Immutability

Strings are immutable — you can't change a character directly:

let msg = "hello";
msg[0] = "H";  // ❌ Invalid
msg = "Hello"; // ✅ Correct way

🧪 Practice Exercise:

Task:

1. Create a string with your full name and print each character using a loop.
2. Count how many times the letter a appears using .split() and .length.
3. Use slice() to extract the first name from a full name.
4. Convert " Welcome! " to "welcome!" (trim + lowercase).
5. Use template literals to print:

Hello, [Your Name]!
Welcome to JavaScript Strings.

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