How to find prime numbers between 0 - 100?

Answer 1

Using Sieve of Eratosthenes, source on Rosettacode

fastest solution: https://repl.it/@caub/getPrimes-bench

function getPrimes(limit) {
    if (limit < 2) return [];
    var sqrtlmt = limit**.5 - 2;
    var nums = Array.from({length: limit-1}, (_,i)=>i+2);
    for (var i = 0; i <= sqrtlmt; i++) {
        var p = nums[i]
        if (p) {
            for (var j = p * p - 2; j < nums.length; j += p)
                nums[j] = 0;
        }
    }
    return nums.filter(x => x); // return non 0 values
}
document.body.innerHTML = `
${getPrimes(100).join(', ')}
`;

// for fun, this fantasist regexp way (very inefficient):
// Array.from({length:101}, (_,i)=>i).filter(n => n>1&&!/^(oo+)\1+$/.test('o'.repeat(n))