# Fibonacci Sequence program in JavaScript

In the Fibonacci sequence is a series, next number is the addition of the last two numbers, the Fibonacci series starts with 0, and 1.

## Fibonacci Series in JavaScript using for loop

In this program, the user will take a length of the series through prompt and find Fibonacci Sequence by using for loop.

<!DOCTYPE html>
<html>
<body>
<script>
function fibonacci()
{
var a=0,b=1,fib=0,n,i;
var n=prompt("Enter the length of series:");
document.write(a+"</br> "+b+"</br>");
for(i=2;i<n;i++)
{
fib=a+b;
document.write(fib+"</br>");
a=b;
b=fib;
}
}
</script>
<form>
<input type="button" value="fibonacci" onclick="fibonacci();">
</form>
</body>
</html>

Input has taken through javascript prompt method

## output

Enter the length of series:9
0
1
1
2
3
5
8
13
21

### Logic to print Fibonacci series for a given length:

• Take a length of series as an input from the user using a javascript prompt and store it in a variable n.
• Fibonacci series starts with 0 and 1, so print 0 and 1 at the beginning which is stored in variables a and b.
• For finding the next term add the previous two-term inside for loop i.e fib=a+b.
• print the current Fibonacci series number i.e fib and for finding the next Fibonacci series number, copy the value of b into a, i.e a=b, and copy the fib value to b, i.e, b=fib inside for loop.

## Program to print Fibonacci Series in JavaScript using while loop

In this program, the user will take a length of the series through prompt and find Fibonacci Sequence by using while loop.

<!DOCTYPE html>
<html>
<body>
<script>
function fibonacci()
{
var a=0,b=1,fib=0,n,i;
var n=prompt("Enter the length of series:");
document.write(a+"</br> "+b+"</br>");
i=2;
while(i<n)
{
fib=a+b;
document.write(fib+"</br>");
a=b;
b=fib;
i++;
}
}
</script>
<form>
<input type="button" value="fibonacci" title="fibonacci series" onclick="fibonacci();">
</form>
</body>
</html>

Input has taken through javascript prompt method

## output

Enter the length of series:10
0
1
1
2
3
5
8
13
21
34