JavaScript Strings | Learn Computer Academy

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

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:

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

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