This article will teach us how to find Prime Numbers in Javascript. Prime numbers are the numbers that have only two factors. They are 1 and itself. We will share two programs in javascript where one will return whether the entered number is a prime number or not and the other one will return the list of prime numbers under the input.

## Prime Numbers in Javascript

### Program to Find whether the Entered Value is a Prime Number or Not

function isPrime(number) { if (number <= 1) { return false; } for (let i = 2; i <= Math.sqrt(number); i++) { if (number % i === 0) { return false; } } return true; } // Example usage: const numToCheck = 17; if (isPrime(numToCheck)) { console.log(`${numToCheck} is a prime number.`); } else { console.log(`${numToCheck} is not a prime number.`); }

In the above program, we have created a function called isPrime() that takes a number as input and returns true if the number is a prime number. We are using one of the native javascript methods Math.sqrt() to determine the square root of the input number. We are checking it in a loop that starts from 2 because 1 will be the default factor of any number.

Once the check is done, we are printing it to the console for our convenience at this point in time.

### Program to Return the List of Prime Numbers up to the entered Input Value

function getPrimesUnderLimit(limit) { const primes = []; for (let i = 2; i < limit; i++) { if (isPrime(i)) { primes.push(i); } } return primes; } function isPrime(number) { if (number <= 1) { return false; } for (let i = 2; i <= Math.sqrt(number); i++) { if (number % i === 0) { return false; } } return true; } // Example usage: const limit = 30; const primeList = getPrimesUnderLimit(limit); console.log(`Prime numbers under ${limit}: ${primeList.join(', ')}`);

In the above program, we are using a function called getPrimeUnderLimit() to return the list of prime numbers under the input given. We are using the above program isPrime() to determine whether the given number is a prime number.

We are using an array primeList[] array to create the list of prime numbers that return from the getPrimeUnderLimit() function and printing it to the console by making it a string that is divided by a comma(,) for our convenience.