JavaScript

In JavaScript, strings are one of the most important data types. A string is a sequence of characters used to store and manipulate text like names, messages, emails, etc.

Let’s explore JavaScript strings in depth with examples, methods, and best practices.

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🔤 What is a String in JavaScript?

A string is any text enclosed in:

• Single quotes: 'hello'
• Double quotes: "world"
• Backticks (template literals): `Hi ${name}`

let name = "John";
let message = 'Welcome to JavaScript';

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🧪 Examples:

let firstName = "Devin";
let greeting = 'Hello, world!';
let sentence = `My name is ${firstName}`;

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📏 String Length

Use .length to find the number of characters in a string:

let text = "JavaScript";
console.log(text.length);  // Output: 10

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🧰 Common String Methods

Method	Description
toUpperCase()	Converts to uppercase
toLowerCase()	Converts to lowercase
charAt(index)	Returns character at given index
indexOf(value)	Finds first index of value
lastIndexOf(value)	Finds last index of value
slice(start, end)	Extracts part of a string
substring(start, end)	Similar to slice
replace(old, new)	Replaces part of a string
includes(value)	Checks if string contains value
trim()	Removes whitespace from both ends
split(separator)	Splits string into an array
concat()	Joins two or more strings

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✨ Examples of String Methods

🔡 1. toUpperCase() & toLowerCase()

let city = "delhi";
console.log(city.toUpperCase()); // DELHI
console.log(city.toLowerCase()); // delhi

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🪓 2. slice()

let lang = "JavaScript";
console.log(lang.slice(0, 4)); // Java

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🔄 3. replace()

let msg = "I love HTML";
console.log(msg.replace("HTML", "JavaScript")); // I love JavaScript

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🔍 4. includes()

let str = "Frontend Development";
console.log(str.includes("Front")); // true
console.log(str.includes("Backend")); // false

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✂️ 5. split()

let data = "apple,banana,mango";
let fruits = data.split(",");
console.log(fruits); // ["apple", "banana", "mango"]

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🧼 6. trim()

let username = "   devin   ";
console.log(username.trim()); // "devin"

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🧵 Template Literals (Backticks)

Backticks (`) allow multi-line strings and embedding variables.

let name = "Amit";
let message = `Hello, ${name}! Welcome to JS.`;
console.log(message); // Hello, Amit! Welcome to JS.

You can also write multi-line strings:

let paragraph = `
This is line 1
This is line 2
This is line 3
`;

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🚨 String Immutability

Strings are immutable in JavaScript — meaning once a string is created, it cannot be changed. You can only create a new string using operations:

let str = "hello";
str[0] = "H";  // ❌ does nothing
str = "Hello"; // ✅ create a new string

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🧠 Practice Exercise

let user = " john doe ";
let cleanUser = user.trim();
let capitalUser = cleanUser.toUpperCase();
console.log(capitalUser); // Output: JOHN DOE

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📌 Summary

• Strings are used to store and manipulate text.
• You can use single, double, or backtick quotes.
• JavaScript provides many powerful methods to work with strings.
• Strings are immutable – every change creates a new string.
• Template literals (`) are modern and recommended for formatting strings with variables.

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