Printing the first n numbers of the Fibonacci sequence

Question

I have written a code below for printing the first n fibonacci numbers,

the code is as follows

var fibo = function (n){
 var num = 1, prevNum = 1, currentNum = 1, printNum = [];
 do{
 if(num == 1){
 prevNum = num;
 currentNum = num;
 printNum.push(num);
 num++;
 }else if(num == 2){
 currentNum = num;
 printNum.push(num);
 num++;
 }else{
 num = currentNum + prevNum;
 printNum.push(num);
 prevNum = currentNum;
 currentNum = num;
 }
 n--;
 }while(n >= 1);
 console.log(printNum.toString());
}
fibo(6);
fibo(10);
fibo(20);

The output of the above program is as follows,

PS D:\> node .\fibonacci.js
1,2,3,5,8,13
1,2,3,5,8,13,21,34,55,89
1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,6765,10946
PS D:\>

Is there a better way in implementing it ?

please review my code

• greybeard: Please add what you used as a reference for the Fibonacci series to generate. What has prompted to first build printNum and only print it when the last element is computed?
• greybeard: (You tagged comparative-review - I find only one solution presented.)

Answer 1

For readability, I prefer the (pythonesque?!) destructuring assignment
(and array over, say, BigUint64Array[n]).
I do not find value added by the name suffix Num.
When not intending to change the meaning of fibo at runtime, I'd rather declare it a function.
Somehow, special cases (1, 2) crept into your implementation.
Separation of concerns would would split out logging - I kept fibo()s interface below:

/** Return an array with the first n elements of the Fibonacci sequence.
 * If the array is non-empty, log it to the console. */
function fibo(n) {
 if (n <= 0)
 return []
 var a = 1, b = 1,
 sequence = [b]
 while (0 < --n) {
 [a, b] = [b, a + b]
 sequence.push(b)
 }
 console.log(sequence.toString())
 return sequence
}
console.log(fibo(0))
fibo(6); fibo(10); fibo(20);

For JSDoc, add tags as you like

 * @argument n the number of elements
 * @return an array with the first n elements of the Fibonacci sequence.

Answer 2

JavaScript number primitives and Number objects use IEEE 754 Floating-Point Arithmetic. The Number.MAX_SAFE_INTEGER constant represents the maximum safe integer in JavaScript (2^53 - 1). Use JavaScript BigInt to avoid floating-point approximations for large integer values. Use JavaScript BigInt to avoid printing large integer values in exponential notation.

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Keep things simple. Why do you complicate the computation with if () else if () else?

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A sequence of Fibonacci numbers has value independent of its String output format. Don't conflate the computation and the toString output of the sequence by doing everything in a single function.

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The On-Line Encyclopedia of Integer Sequences (OEIS) definition of Fibonacci numbers:

OEIS: A000045 
Fibonacci numbers: F(n) = F(n-1) + F(n-2) with F(0) = 0 and F(1) = 1.
https://oeis.org/A000045

In JavaScript, a sequence of n Fibonacci numbers:

function fibonacci(n) {
 let fibs = [];
 let [a, b] = [BigInt(0), BigInt(1)];
 for (let i = 0; i < n; i++) {
 fibs.push(a);
 [a, b] = [b, a + b];
 }
 return fibs;
}
console.log(fibonacci(150).toString());

---

0,1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,
. . .
,10284720757613717413913,16641027750620563662096,26925748508234281076009

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An older Fibonacci number definition starts the sequence with 1, 1.

let [a, b] = [BigInt(1), BigInt(1)];

Fibonacci started the sequence with with 1, 2.

let [a, b] = [BigInt(1), BigInt(2)];

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Answer 3

 n--;
}while(n >= 1);

You don't need to consume the input argument. You already have an up-to-date value.

 } while (n > printNum.length);

If you start with

 const printNum = [1, 2];

You can close with

 return printNum.slice(0, n);

Then you don't need any special cases. Just

 const fibs = [1, 2];
 while (fibs.length < n) {
 fibs.push(fibs[fibs.length - 1] + fibs[fibs.length - 2]);
 }
 return fibs.slice(0, n);

Note that this also gets rid of the redundant variables and just works on the array.