Steps to Find the Fibonacci Series of n Numbers

Step 1: Take the first elements of the sequence to be 0 and the second element as 1.

Step 2: Sum up the first and second elements; the result is our third element.

Step 3: Now take the second and third elements and add them; the result is our fourth element.
 Step 4: Repeat this process till n numbers are generated.
In general, the n_{th }number of the series is equal to the (n1)_{th }+ (n2)_{th }number.
Examples of Fibonacci Series in JavaScript
A Fibonacci series in JavaScript is written as following:
0, 1, 1, 2, 3, 5, 8, 13, 21, 34 and so on.
As we have seen, the Fibonacci sequence is the integer sequence in which the first two terms are 0 and 1. After that, the following term is defined as the sum of the previous two terms. Having this piece of information, let's start to code the Fibonacci series in JavaScript.
Get Fibonacci Series up to N terms
Here in the below code, We have received the input in the variable N, which holds the value up to which we need to find the Fibonacci. Later we declared the first two known terms of the Fibonacci series, and then we iterated until the required number of terms weren't generated in the output. And then Constantly updating the fn1 and fn2 variables.
const N = parseInt(prompt('Enter the number of terms: '));
let fn1 = 0, fn2 = 1, nextFibonacci;
console.log('Fibonacci Series upto N terms is:');
for (let i = 1; i <= N; i++) {
console.log(fn1);
nextFibonacci = fn1 + fn2;
fn1 = fn2;
fn2 = nextFibonacci;
}
Output
Enter the number of terms: 6
Fibonacci Series up to N terms is:
0
1
1
2
3
5
The user is requested in the above code to input the number of terms they want in the Fibonacci series in JavaScript.
The for loop repeats until the condition of for loop is failed.
The value 0 is printed first. The value of the second term is then saved in variable fn1 in each iteration, while the total of the two preceding terms is stored in variable fn2.
Now as we understood how we code the Fibonacci till N terms, let's move on to the next section to check out another version of the question based on the Fibonacci series in JavaScript.
Get Fibonacci Series of the first 8 terms
Here in the below code, We declared the first two known terms of the Fibonacci series, and then we iterated until 8 numbers of the sequence were generated in the output. And then Constantly updating the fn1 and fn2 variables.
let fn1 = 0, fn2 = 1, nextFibonacci;
console.log('Fibonacci Series upto 8 terms is:');
for (let i = 1; i <= 8; i++) {
console.log(fn1);
nextFibonacci = fn1 + fn2;
fn1 = fn2;
fn2 = nextFibonacci;
}
Output
Fibonacci Series upto 8 terms is:
0
1
1
2
3
5
8
13
Get the Sum of the First 7 Terms of the Fibonacci Series
Here in the below code, We declared the first two known terms of the Fibonacci series and a sum variable which was initialized to zero. Then we iterated until 7 numbers of the sequence were generated. We always added the current variable of the series to sum and updated the fn1 and fn2 variables.
let fn1 = 0, fn2 = 1, nextFibonacci, sum = 0;
console.log('Sum of the first 7 terms of the Fibonacci series is:');
for (let i = 1; i <= 7; i++) {
sum = sum + fn1;
nextFibonacci = fn1 + fn2;
fn1 = fn2;
fn2 = nextFibonacci;
}
console.log(sum);
Output
Sum of the first 7 terms of the Fibonacci series is:
20
Get the Fibonacci Series using the Recursion Function
Here in the below code, We declared the first two known terms of the Fibonacci series, and then we iterated until the desired numbers of the sequence were generated in the output. During each iteration, we called the function to generate the N_{th }fibonacci number using a function call.
During every function call, we made a call to generate the (n1)_{th }and (n2)_{th }number which recursively went on till we reached either the first or the second number of the series where we return the number itself.
function nthFibonacci(currNum) {
if(currNum <= 1) {
return currNum;
}
else {
return nthFibonacci(currNum1) + nthFibonacci(currNum  2);
}
}
const N = parseInt(prompt('Enter the number of terms: '));
let fn1 = 0, fn2 = 1, nextFibonacci;
console.log('Fibonacci Series upto N terms is:');
for (let i = 0; i < N; i++) {
console.log(nthFibonacci(i));
}
Output
Enter the number of terms: 10
Fibonacci Series upto N terms is:
0
1
1
2
3
5
8
13
21
34
Get the Fibonacci Series in Reverse Order
Here in the below code, We declared an array to store the series, We updated first and second variables of the array of 0 and 1 since they are the first two numbers in the sequence. We iterated till N numbers were generated and updated the current position in the array to the sum of last 2 positions.
In the end, we started from N1 and iterated over the array in reverse order till the 0_{th }index to print the fibonacci sequence in reverse order.
const N = parseInt(prompt('Enter the number of terms: '));
console.log('Fibonacci Series upto N terms in reverse order is:');
let a = [];
a[0] = 0;
a[1] = 1;
for (let i = 2; i < N; i++) {
a[i] = a[i2] + a[i1];
}
for (let i = N1; i >= 0; i) {
console.log(a[i]);
}
Output
Fibonacci Series upto N terms in reverse order is:
13
8
5
3
2
1
1
0
Frequently Asked Questions
How to implement Fibonacci in JavaScript?
To implement Fibonacci in JavaScript, create a function that starts with two variables (0 and 1), then iteratively adds them while storing the previous two values in a loop, and returns the result.
What is the Fibonacci series used for?
The Fibonacci series is used in various fields like mathematics, computer science, and nature modeling to describe growth patterns, sequences, and algorithms, aiding in problemsolving and data analysis.
How do you use the Fibonacci algorithm?
To use the Fibonacci algorithm, you apply it in coding or calculations by calling a function that generates Fibonacci numbers to solve problems involving sequences, patterns, or mathematical relationships.
How many variables are needed to find Fibonacci series?
Generally, 3 variables are declared. 2 variables can be initialized as the first(value = 0) and the second term(value = 1) of the series and the 3rd variable can be used to keep track of the length of the Fibonacci sequence to be printed.
How does Fibonacci sequence work in JavaScript?
Just like in any other programming language, a Fibonacci series in JavaScript is numerical series that starts with two fixed numbers 0 and 1. All the following numbers of the series can be generated using the sum of the last two numbers.
Which algorithm is widely used for Fibonacci series in JavaScript?
Generally loops are used to generate Fibonacci series in javaScript. You can use a for loop or a while loop according to your convenience.
Conclusion
In this article, we have extensively discussed the problem Fibonacci series in JavaScript.
To learn more about Javascript, see the Importance of JavaScript, Javascript Interview Questions.
Also read: fibonacci series in c
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