Fibonacci series implementation in JavaScript

Fibonacci Series is a series in which the next number of the series is the sum of the previous 2 numbers. For example :- 0, 1, 1, 2, 3, 5, 8...

Took 3 minutes and 15 seconds to code fibonacci series using JavaScript. Here is the code snippet.

Code:

function printFibonacciSeries() {

var first_num = 1;

var second_num = 1;

document.getElementById('demo').innerHTML +=

first_num + "<br>" + second_num + "<br>";

for (var i = 0; i < 12; i++) {

third_num = first_num + second_num;

document.getElementById('demo').innerHTML += third_num + '<br>';

first_num = second_num;

second_num = third_num;

}

}

printFibonacciSeries();

Result:

1
1
2
3
5
8
13
21
34
55
89
144
233
377