Find the Nth Number of Fibonacci series using JavaScript

Here’s some fun finding the Nth number of a Fibonacci series using JavaScript Recursion

<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<title>Nth Fibonacci Series</title>
<script type="text/javascript">
function callFibo() {
//extract textbox value
var num = document.getElementById('txtFibo').value;
//check if it is a number and greater than 1 and less than 36
if (isNaN(num) ((num < 1) (num > 35))) {
alert("Only numbers allowed. Enter a number > 0 and < 35");
}
else {
alert("Number " + num + " in the Fibonacci series is " +
calcFiboNth(num));
}
}

function calcFiboNth(num) {
if (num > 2) {
return calcFiboNth(num - 2) + calcFiboNth(num - 1);
} else {
return 1;
}
}
</script>
</head>

<body>
<input id="txtFibo" type="text" />
<br /><br />
<input id="btnFibo" type="button" value="Enter a Number and click"
onClick="callFibo()" />
</body>
</html>


The function calcFiboNth() makes a recursive call to itself each time with a different ‘num’ value and this continues till ‘num’ reaches 1. That’s how you get the Nth number of the series.

Note: It is a good idea to add an upper limit to the number entered. Entering a higher number could take a very long time to compute the nth number of the Fibonacci series.

image

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About The Author

Suprotim Agarwal
Suprotim Agarwal, Developer Technologies MVP (Microsoft Most Valuable Professional) is the founder and contributor for DevCurry, DotNetCurry and SQLServerCurry. He is the Chief Editor of a Developer Magazine called DNC Magazine. He has also authored two Books - 51 Recipes using jQuery with ASP.NET Controls. and The Absolutely Awesome jQuery CookBook.

Follow him on twitter @suprotimagarwal.

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