Sieve of Eratosthenes Javascript version

Sieve of Eratosthenes.js

var sieve = function(num) {
    var arr = [],
        primes = [],
        i = 0,
        curPrime;

    num = parseInt(num);
    if (isNaN(num) || num < 2) {
        return primes;
    }


    for (; i < num - 1; i++) {
        arr[i] = i + 2;
    }

    while (arr[0]) {
        primes.push((curPrime = arr[0]));
        arr = arr.slice(1).filter(function(i) {
            return i % curPrime !== 0;
        });
    }
    return primes;
};