JavaScript program to print Fibonacci series

This is another interesting program which is very useful for school and college students. This program sometimes asked in Interviews for Fresher, so be prepare yourself for the future.

If you don’t know what is Fibonacci series, here is the small example,

0, 1, 1, 2, 3, 5, 8…

0,1 -> 0 +1 =1 ( 1 is the next number)
0,1,2 -> 1+1 = 2 (2 is the next number)
0,1,2 -> 1+2 = 3
0,1,2,3 -> 2+3 = 5

So basically Fibonacci series is finding the next number by adding the first two numbers

Here is the JavaScript function to find the Fibonacci series function:

function fibonacciSeries(limit)
{
	var first_num = 0, second_num = 1, next_num, outputElement;

	if(limit != '')
	{
		outputElement = document.getElementById("output"); 
		
		outputElement.innerHTML = "";
		outputElement.innerHTML = "<br>";
		outputElement.innerHTML += first_num + "<br>";
		outputElement.innerHTML += second_num + "<br>";
		
		/* here we are checking > 2 because 
		   we have already printed two numbers 
		   of fiboncacci series above
		*/
		//loop through the limit till it becomes 0 (zero)
		while(limit > 2)
		{       
		   //add the first value and second to get the next value
		   next_num   = first_num + second_num;
		   
		   //assign second value to first
		   //next value to second
		   //to find the next series
		   first_num  = second_num;
		   second_num = next_num;
		   
		   //print the next value
		   outputElement.innerHTML += next_num + "<br>";
		   
		   //decrement the limit by one 
		   limit--;
		}
	}else{
		document.getElementById("output").innerHTML = "Please enter a value!";
	}
}

The above program is self explanatory, read the comments in the script. This function accepts limit as a parameter,

fibonacciSeries(10) -> this will print 10 values of Fibonacci series

Here is the usage example of the above fibonacci function:

<html>
	<head>
		<title>Fibonacci series in pure JavaScript - Tutorialsmade.com</title>
		<script>
			//fibonacci series in pure JavaScript
			//by tutorialsmade.com
			
			function getFibonacci()
			{
				//get the limit from textbox
				var limit = document.getElementById("limit").value;
				
				//call the fibonacci function
				fibonacciSeries(limit);
			}
			function fibonacciSeries(limit)
			{
				var first_num = 0, second_num = 1, next_num, outputElement;

				if(limit != '')
				{
					outputElement = document.getElementById("output"); 
					
					outputElement.innerHTML = "";
					outputElement.innerHTML = "<br>";
					outputElement.innerHTML += first_num + "<br>";
					outputElement.innerHTML += second_num + "<br>";
					
					/* here we are checking > 2 because 
					   we have already printed two numbers 
					   of fiboncacci series above
					*/
					//loop through the limit till it becomes 0 (zero)
					while(limit > 2)
					{       
					   //add the first value and second to get the next value
					   next_num   = first_num + second_num;
					   
					   //assign second value to first
					   //next value to second
					   //to find the next series
					   first_num  = second_num;
					   second_num = next_num;
					   
					   //print the next value
					   outputElement.innerHTML += next_num + "<br>";
					   
					   //decrement the limit by one 
					   limit--;
					}
				}else{
					document.getElementById("output").innerHTML = "Please enter a value!";
				}
			}
		</script>
	</head>
	<body>
		<h2>Fibonacci series in pure JavaScript - Tutorialsmade.com</h2>
		<h3>Enter the limit:</h3>
		<input type="text" id="limit" />
		<button onclick="getFibonacci()" >Print Fibonacci Series</button>

		<h4>Output: <span id="output"></span></h4>
	</body>
</html>

On click of the button, getFibonacci() function will be called, then fibonacciSeries(limit) will be called by getFibonacci() by sending the limit value from text box.
Here is the live Demo of JavaScript Fibonacci series: