JavaScript Basics

Write a JavaScript program to display Hello World

Description: Write a JavaScript program that prints “Hello, World!” in the console.

Hint:

• Use console.log().
• Text must be inside quotes.

JavaScript Hello World program

console.log("Hello, World!");

Output:

How it works

• console.log() prints a message in the browser console (press F12 to open it).
• The text is a string, so it is written in quotes.

Read JavaScript Basic Program.

Write a JavaScript program to add two numbers

Description: Store two numbers in variables and print their sum.

Hint:

• Use let or const for the variables.
• Use the + operator.

JavaScript program to add two numbers

const a = 12;
const b = 8;
const sum = a + b;

console.log(`Sum of ${a} and ${b} is ${sum}`);

Output:

How it works

• The + operator adds two numbers.
• A template literal with ${ } puts the values inside the text.

Read JavaScript Operators. If the numbers come from prompt() or an input box, convert them with Number() first, otherwise "12" + "8" gives "128".

Write a JavaScript program to swap two variables

Description: Swap the values of two variables a and b.

Hint:

• The old way uses a third variable.
• The modern way uses array destructuring.

JavaScript program to swap two variables

let a = 10;
let b = 20;
console.log("Before:", a, b);

[a, b] = [b, a];

console.log("After:", a, b);

Output:

How it works

• The right side [b, a] makes a new array with the two values.
• The left side [a, b] destructures it back into the variables, so they are swapped in one line.

Read ES6 Features.

Write a JavaScript program to check even or odd number

Description: Check whether a number is even or odd.

Hint:

• A number is even if the remainder after dividing by 2 is 0.

JavaScript program for even or odd

function checkEvenOdd(n) {
  if (n % 2 === 0) {
    return n + " is even";
  }
  return n + " is odd";
}

console.log(checkEvenOdd(4));
console.log(checkEvenOdd(7));

Output:

How it works

• % gives the remainder: 4 % 2 is 0 and 7 % 2 is 1.
• The function returns a text for each case.

Read Conditional Statements.

Write a JavaScript program to find the largest of three numbers

Description: Find the largest of the three numbers 25, 78 and 42.

Hint:

• Compare with if and &&.
• Or use Math.max().

JavaScript program for the largest of three numbers

const a = 25, b = 78, c = 42;

let largest;
if (a >= b && a >= c) {
  largest = a;
} else if (b >= a && b >= c) {
  largest = b;
} else {
  largest = c;
}

console.log("Largest:", largest);
console.log("Using Math.max:", Math.max(a, b, c));

Output:

How it works

• The first if checks if a is at least as big as both others.
• Math.max() does the same in one call.

Write a JavaScript program to check leap year

Description: Check if a year is a leap year.

Hint:

• Divisible by 4 and not by 100, or divisible by 400.

JavaScript program to check a leap year

function isLeap(year) {
  return (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;
}

for (const y of [2024, 1900, 2000, 2023]) {
  console.log(y + (isLeap(y) ? " is a leap year" : " is not a leap year"));
}

Output:

How it works

• 1900 is divisible by 100 but not by 400, so it is not a leap year.
• The ternary operator picks the text.