JavaScript Program to print Fibonacci Series

The Fibonacci sequence is the integer sequence where the first two terms are 0 and 1. After that, the next term is defined as the sum of the previous two terms.

The sequence Fn of Fibonacci numbers is defined by the recurrence relation:

Fn = Fn-1 + Fn-2 with seed values F0 = 0 and F1 = 1

Examples:

Input : 5 
Output : 8

Input :8
Output :34

There are three methods to print the Fibonacci series, which are described below:

Approach 1: Using for loop

Example: This example uses for loop to print the Fibonacci series.

javascript

function fibonacci(num) {
    let num1 = 0;
    let num2 = 1;
    let sum;
    let i = 0;
    for (i = 0; i < num; i++) {
        sum = num1 + num2;
        num1 = num2;
        num2 = sum;
    }
    return num2;
}

console.log("Fibonacci(5): " + fibonacci(5));
console.log("Fibonacci(8): " + fibonacci(8));

Output:

Fibonacci(5): 3
Fibonacci(8): 13

Approach 2: Using while loop

Example: This example uses a while loop to print the Fibonacci series.

javascript

function fibonacci(num) {
    if (num == 1)
        return 0;
    if (num == 2)
        return 1;
    let num1 = 0;
    let num2 = 1;
    let sum;
    let i = 2;
    while (i < num) {
        sum = num1 + num2;
        num1 = num2;
        num2 = sum;
        i += 1;
    }
    return num2;
}

console.log("Fibonacci(5): " + fibonacci(5));
console.log("Fibonacci(8): " + fibonacci(8));

Output:

Fibonacci(5): 3
Fibonacci(8): 13

Approach 3: using recursion

As we know that the nth Fibonacci number is the summation of n-1 and n-2 term and the n-1 term is the summation of n-2 and n-3 terms. So, to get the nth Fibonacci term we can follow fib(n)=fib(n-1)+fib(n-2) fib(n)=fib(n-2)+fib(n-3)+fib(n-3)+fib(n-4) …. fib(n)=fib(1)+fib(0)+fib(1)+fib(0)+fib(1)+fib(0)….fib(1)+fib(0) [terms containing sum of fib(1) and fib(0) fib(1)=0 fib(2)=1

Example: This example shows the use of the above approach.

javascript

function fibonacci(num) {
    if (num == 1)
        return 0;
    if (num == 2)
        return 1;
    return fibonacci(num - 1) + fibonacci(num - 2);
}
console.log("Fibonacci(5): " + fibonacci(5));
console.log("Fibonacci(8): " + fibonacci(8));

Output:

Fibonacci(5): 3
Fibonacci(8): 13