var getPrimes = function (n) {
    var numbers = [],
        multiple, i, j, len,
        square = function (x) { return x * x; };
        
    for(i = 2; i <= n; i++) {
        numbers.push(i);
    }
    
    for(j = 0; square(numbers[j]) < n; j++) {
        multiple = numbers[j];
        for(i = 0, len = numbers.length; i < len; i++) {
            if(numbers[i] % multiple === 0) {
                if(numbers[i] === multiple) { i++; continue; }
                numbers.splice(i, 1);
            }
        }
    }
    return numbers;
};

var getPrimes = function (n) {
    var numbers = [],
        multiple, i, j,
        square = function (x) { return x * x; };
        
    for(var i = 2; i <= n; i++) {
        numbers.push(i);
    }
    
    j = 0;
    while(square(numbers[j]) < n) {
        multiple = numbers[j];
        
        i = 0;
        while(i < numbers.length) {	
            if(numbers[i] % multiple === 0) {
                if(numbers[i] === multiple) { i++; continue; }
                numbers.splice(i, 1);
            }
            i++;
        }
        j++;
    }
    
    return numbers;
};

Returns an array of all the prime numbers up to (n) using an implementation of the Sieve of Eratosthenes.

Sieve of Eratosthenes

math

JavaScript