JavaScript Loops

Write a JavaScript program to print the multiplication table of a number

Description: Print the multiplication table of 7, from 1 to 10.

Hint:

• Use a for loop from 1 to 10.

JavaScript multiplication table program

const num = 7;

for (let i = 1; i <= 10; i++) {
  console.log(`${num} x ${i} = ${num * i}`);
}

Output:

How it works

• The loop runs with i from 1 to 10.
• The template literal prints the line with the numbers.

Read JavaScript Loops.

Write a JavaScript program to find the factorial of a number

Description: Find the factorial of 5 in two ways: with a loop and with a recursive function.

Hint:

• Factorial of 5 is 5 x 4 x 3 x 2 x 1 = 120.
• A recursive function needs a base case.

JavaScript factorial program

// loop
let fact = 1;
for (let i = 1; i <= 5; i++) {
  fact *= i;
}
console.log(fact);

// recursion
function factorial(n) {
  if (n <= 1) return 1;       // base case
  return n * factorial(n - 1);
}
console.log(factorial(5));

Output:

How it works

• The loop multiplies fact with 1, 2, 3, 4 and 5.
• The recursive function calls itself with a smaller number until it reaches the base case.

Read JavaScript Functions.

Write a JavaScript program to print the Fibonacci series

Description: Print the first 10 numbers of the Fibonacci series.

Hint:

• Each number is the sum of the two before it.
• Start with 0 and 1.

JavaScript Fibonacci program

let a = 0, b = 1;
const series = [];

for (let i = 0; i < 10; i++) {
  series.push(a);
  [a, b] = [b, a + b];
}

console.log(series.join(", "));

Output:

How it works

• [a, b] = [b, a + b] moves to the next pair.
• join(", ") makes one text from the array.

Write a JavaScript program to check prime number

Description: Check whether the numbers 2, 15, 17 and 1 are prime.

Hint:

• A prime number is greater than 1 and has no divisor other than 1 and itself.
• Test divisors up to the square root.

JavaScript prime number program

function isPrime(n) {
  if (n < 2) return false;
  for (let i = 2; i <= Math.sqrt(n); i++) {
    if (n % i === 0) return false;
  }
  return true;
}

for (const n of [2, 15, 17, 1]) {
  console.log(n + (isPrime(n) ? " is prime" : " is not prime"));
}

Output:

How it works

• Numbers below 2 are not prime.
• For 15 the loop finds that 15 % 3 === 0 and returns false.
• As soon as one divisor is found, the function returns.