JavaScript code to generate prime number series

Took only 55 seconds to code JavaScript prototype to generate prime number series. Here is the code snippet.

Code (Run Code):

arr = [];

function checkPrime(num) {

if (num == 1) {

return false;

} else if (num == 2) {

return true;

}

for (var x = 2; x < num; x++) {

if (num % x == 0) {

return false;

}

}

return true;

}

function primeNumbers() {

num = Number(document.getElementById('number').value);

for (var j = 1; j < num; j++) {

if (checkPrime(j)) {

arr.push(j);

}

}

document.getElementById('result').innerHTML = arr;

}