JavaScript Lecture: Chapter 3 - Loops and Strings

Overview

• Welcome to the Complete JavaScript Series
• Covering JavaScript from zero to advanced
• Today: Chapter 3 (Loops and Strings)
• Topics: Loops and Strings, Practical Exercises, Project Applications

Resources

• All lecture notes available in the description box
• Access the full playlist for all JavaScript series lectures and practice questions

Loops in JavaScript

Introduction to Loops

• Essential for repeating tasks in programming
• Executes a piece of code repeatedly
• Examples: Playing a song on loop, repeating actions

Types of Loops

1. For Loop
2. While Loop
3. Do-While Loop
4. For-of Loop
5. For-in Loop

For Loop

• Syntax: for (initialization; stopping condition; updation) { block of code }
• Example: for (let count = 1; count <= 5; count++) { console.log("Apna College"); }
• Steps:
  • Initialization: let count = 1
  • Stopping Condition: count <= 5
  • Updation: count++
  • Block of Code: console.log("Apna College")

While Loop

• Syntax: while (condition) { block of code }
• Example: let i = 1; while (i <= 5) { console.log("Apna College"); i++; }
• Executes block of code until the condition is false

Do-While Loop

• Syntax: do { block of code } while (condition);
• Guarantees the loop runs at least once
• Example: let i = 0; do { console.log("Apna College"); i++; } while (i < 5);

For-of Loop

• Used to iterate over iterable objects (like arrays or strings)
• Syntax: for (let variable of iterable) { block of code }
• Example: let str = "JavaScript"; for (let char of str) { console.log(char); }
• Ideal for strings and arrays

For-in Loop

• Used for iterating over object properties
• Syntax: for (let key in object) { block of code }
• Example: let student = { name: "Rahul", age: 20, isPass: true }; for (let key in student) { console.log(key + ": " + student[key]); }

Practical Examples and Exercises

Example 1: Sum of First n Numbers

• Problem: Calculate the sum from 1 to n
• Solution: Using For Loop let sum = 0; let n = 5; for (let i = 1; i <= n; i++) { sum += i; } console.log("Sum: " + sum); // Sum: 15

Example 2: Print Even Numbers from 0 to 100

• Problem: Print all even numbers between 0 to 100
• Solution: Using For Loop and Conditional Check for (let num = 0; num <= 100; num++) { if (num % 2 === 0) { console.log(num); } }

Example 3: Simple Number Guessing Game

• Problem: Create a game where users guess a number until correct
• Solution: Using While Loop and Prompt let gameNumber = 25; let userGuess; while (userGuess != gameNumber) { userGuess = prompt("Guess the game number:"); if (userGuess == gameNumber) { console.log("Congratulations, you guessed the right number!"); } else { console.log("Wrong guess! Try again."); } }

Strings in JavaScript

What are Strings?

• Sequence of characters used to represent text
• Creation: let str1 = "Hello"; // double quotes let str2 = 'World'; // single quotes
• Can also use backticks for Template Literals let str3 = `Template Literals`;

Important String Properties and Methods

• length: Returns the length of the string let str = "Hello"; console.log(str.length); // 5
• toUpperCase(): Converts string to uppercase console.log(str.toUpperCase()); // HELLO
• toLowerCase(): Converts string to lowercase console.log(str.toLowerCase()); // hello
• trim(): Removes whitespace from both ends of string let str = " Hello World! "; console.log(str.trim()); // "Hello World!"
• slice(): Extracts a part of the string let str = "Hello World"; console.log(str.slice(0, 5)); // Hello
• concat(): Combines two or more strings let str1 = "Hello"; let str2 = "World"; let result = str1.concat(" ", str2); console.log(result); // Hello World // Or simply using + console.log(str1 + " " + str2); // Hello World
• replace(): Replaces a substring within string let str = "Hello"; console.log(str.replace("H", "Y")); // Yello
• charAt(): Returns the character at specified index let str = "Hello"; console.log(str.charAt(1)); // e

Practical String Example: Generate Username

Problem

• Prompt user to enter full name without spaces
• Generate a username in the format @fullname[length]

Solution

Conclusion

• Covered essential concepts of Loops and Strings in JavaScript
• Practiced with relevant examples and exercises
• Encouraged to explore more through additional resources