# Generate a Fibonacci sequence

Posted on • tagged with #javascript

The Fibonacci sequence is a series of numbers where each number in the sequence is the sum of the two preceding numbers. This sequence begins with 0 and 1. In mathematics, the Fibonacci numbers form the sequence, where numbers (n) are greater than 1 (n > 1).

To better understand how the fibonacci numbers are created in the sequence, view the below equation for generating any number in the fibonacci sequence.

F

_{n}= F_{n-1}+ F_{n-2}

## Generate the sequence

Now that the underlying mathematical equation for generating the Fibonacci sequence is known, let's write a JavaScript function to create it.

`function fibonacciSeq(n) {`

let arr = [0, 1];

let num = 0;

for (var i = 1; i < n; i++) {

num = arr[i] + arr[i-1];

arr.push(num);

}

return arr;

}

The above function `fibonacciSeq`

accepts one parameter, the amount of fibonacci numbers to generate in the sequence and returns an array containing the fibonacci sequence. For example, passing in `n = 7`

will generate the following sequence:

`console.log(fibonacciSeq(7));`

// [0, 1, 1, 2, 3, 5, 8, 13]

### Sum the sequence

You can sum the values in a fibonacci sequence fairly quickly with `reduce`

. Using a `for`

loop would also work (and in some cases is more performant than `reduce`

).

`function fibonacciSum(n) {`

let arr = [0, 1];

let num = 0;

for (var i = 1; i < n; i++) {

num = arr[i] + arr[i-1];

arr.push(num);

}

return arr.reduce((a, b) => a + b);

}