JavaScript Program to Print Prime Numbers from 1 to N

A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. In this article, we'll explore how to create a JavaScript program to print all prime numbers from 1 to a given number N.

To find prime numbers from 1 to N, we need to:

• Iterate through all numbers from 2 to N (since 1 is not a prime number).
• For each number, check if it is divisible by any number other than 1 and itself.
• If a number is only divisible by 1 and itself, it is a prime number.

Print Prime Numbers from 1 to N using Basic Approach

Here's a simple implementation to find and print prime numbers from 1 to N. The below code consists of two functions: isPrime and printPrimeNumbers.

• isPrime(num) function: This function checks if a given number num is a prime number or not. It iterates from 2 to the square root of num (inclusive) and checks if num is divisible by any of these numbers. If it is, the function returns false, indicating that num is not a prime number. If num is not divisible by any number in the range, the function returns true, but only if num is greater than 1 (since 1 is not considered a prime number). This is an efficient way to check for primality, as it reduces the number of iterations needed.
• printPrimeNumbers(n) function: This function prints all prime numbers up to a given number n. It iterates from 2 to n and uses the isPrime function to check if each number is prime. If a number is prime, it is printed to the console.

function isPrime(num) {
    for (let i = 2; i <= Math.sqrt(num); i++) {
        if (num % i === 0) {
            return false;
        }
    }
    return num > 1;
}

function printPrimeNumbers(n) {
    for (let i = 2; i <= n; i++) {
        if (isPrime(i)) {
            console.log(i);
        }
    }
}

printPrimeNumbers(100);

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Print Prime Numbers from 1 to N using Array Methods

You can also use JavaScript array methods to make the code more concise. This code defines two functions, printPrimeNumbers and isPrime, to print all prime numbers up to a given number n. The isPrime function checks if a number is prime, while printPrimeNumbers generates an array of numbers from 1 to n, filters out non-prime numbers, and prints the prime numbers.

function printPrimeNumbers(n) {
    Array.from({length: n}, (_, i) => i + 1)
         .filter(isPrime)
         .forEach(prime => console.log(prime));
}

function isPrime(num) {
    return num > 1 && Array.from(
        {length: Math.sqrt(num)}, (_, i) => i + 2)
        .every(divisor => num % divisor !== 0);
}

printPrimeNumbers(100);

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97

The Array.from() method is used to generate an array of numbers from 1 to N, filter() is used to keep only the prime numbers, and forEach() is used to print each prime number.