JS Function for seeking the biggest number in array fails when the first element is undefined or NaN

Question

I have the following function:

const biggestNumOfArray = (array) => {
  if (Array.isArray(array)) {
    let biggest = array[0];
    for (i=0; i < array.length; i++) {
      if (array[i] > biggest) {
        biggest = array[i];
      }
    }
    return biggest;
  } else {
    return NaN;
  }
}

It's purpose is to output the biggest number in an array, ignoring non-number values, and return NaN if it isn't an array.

However, consider the following array:

let myArray = [undefined, 8, 74, -22, 269.64, 92];

All of a sudden, it outputs not 269.64, but undefined.

See, if the first element in an array is undefined or NaN, the variable biggest gets stuck on it, as number > NaN and number > undefined on line 5 will always be false, which means the line to change the biggest to the current will never be executed. How do I avoid that?

Note that this doesn't happen with undefineds that aren't first, as number > undefined also outputs false, unallowing to change the biggest to it.

I tried to change the check for the number being the current biggest, by changing it to array[i] > biggest && array[i] != null, using abstract equality to check for it being undefined or null, but it didn't work - I still got back undefined. It also wouldn't cover NaN.

@epascarello `array[i] > biggest && !(isNaN(array[i]))` doesnt work — danik0011, Jun 30 '23 at 17:55
https://stackoverflow.com/questions/2652319/how-do-you-check-that-a-number-is-nan-in-javascript — epascarello, Jun 30 '23 at 17:55
instead if `let biggest = array[0];` as its initial value you should do something like `let biggest = 0;` or something like that, assuming that you have at least one positive element in your array — Chris G, Jun 30 '23 at 17:57
You are going to have to change your check for array[0] so that is a number... — epascarello, Jun 30 '23 at 17:57
@Kinglish array[0] || 0 works, thanks. except if the first element is undefined and all numbers in the array are less than 0. fix that and you can post it as an answer. also explain how it works. — danik0011, Jun 30 '23 at 18:00
@GabrielePetrioli your answer works, post it as an answer. except you need one "=" and not 3. — danik0011, Jun 30 '23 at 18:01
No `|| 0` is wrong... bad assumption that all the numbers are positive... lol — epascarello, Jun 30 '23 at 18:02
@danik0011 Are you asking about why _your_ function is not working, or just how to do this? — Darryl Noakes, Jun 30 '23 at 18:11
If you want a simple method of just doing it, `Math.max(...array.filter((v) => v != null && !isNaN(v)))` should work. — Darryl Noakes, Jun 30 '23 at 18:12
So... this is a self-challenge and you need/needed help fixing a bug in your code? — Darryl Noakes, Jun 30 '23 at 18:41
@DarrylNoakes Yes but 0 is greater than -100 `let myArray = [undefined, -8, -74, -22, -269.64, -92];` so what would the result be if you set it to zero? — epascarello, Jun 30 '23 at 18:57
Sorry, forgot it was being used as the starting value :facepalm: — Darryl Noakes, Jun 30 '23 at 19:00

Nina Scholz · Answer 1 · 2023-06-30T19:58:14.647

2

You could check for finiteness (Number.isFinite) and take only relevant values for checking the biggest value.

const biggestNumOfArray = (array) => {
  let biggest = undefined;
  if (Array.isArray(array)) {
    for (let i = 0; i < array.length; i++) {
      if (!Number.isFinite(array[i])) continue;
      if (biggest === undefined || array[i] > biggest) biggest = array[i];
    }
  }
  return isFinite(biggest) ? biggest : NaN;
};

const myArray = [undefined, 8, 74, -22, 269.64, 92];

console.log(biggestNumOfArray(myArray));

edited Jun 30 '23 at 19:58

answered Jun 30 '23 at 17:59

Nina Scholz

376,160
25
347
392

i already found `let biggest = -Infinity` to work for me, but i'll take the `isFinite` and a dd it to the code. – danik0011 Jun 30 '23 at 18:04
@danik0011 what if all the numbers are undefined? The max would be `-Infinity` :) Got to love edge cases. lol – epascarello Jun 30 '23 at 18:05
lol wait does `isFinite(-Infinity)` return true? – danik0011 Jun 30 '23 at 18:09
then ill use `typeof biggest = 'number'` – danik0011 Jun 30 '23 at 18:10
No; `isFinite(Infinity)`, `isFinite(-Infinity)`, and `isFinite(undefined)` all return `false`. However, `isFinite(null)` returns `true`. – Darryl Noakes Jun 30 '23 at 18:20
Note also that `null` is equivalent to `0` when comparing using "greater than" and co. Comparisons with `undefined` are always false. – Darryl Noakes Jun 30 '23 at 18:24
1

please see edit. – Nina Scholz Jun 30 '23 at 19:55
Hey, neat! I didn't know the global function(s) and the one(s) on Number were different. – Darryl Noakes Jul 01 '23 at 04:03

score 1 · Answer 2 · answered Jun 30 '23 at 18:15

1

A simpler method would be to use Array#filter to get rid of non-numeric values, then use spread syntax to pass the rest of the values as separate arguments to Math.max.

const biggestNumOfArray = arr => Array.isArray(arr) ? 
  Math.max(...arr.filter(x => !isNaN(x))) : NaN;

console.log(biggestNumOfArray([undefined, 8, 74, -22, 269.64, 92]));

answered Jun 30 '23 at 18:15

Unmitigated

76,500
11
62
80

i know but i decided to do it without Math.max, as a challenge :D – danik0011 Jun 30 '23 at 18:22

score 0 · Answer 3 · answered Jun 30 '23 at 18:16

0

//Nullish coalescing operator
const biggestNumOfArray = (array) => {
  if (Array.isArray(array)) {
    let biggest = array[0] ?? 0;
    for (i = 0; i < array.length; i++) {
      if (array[i] > biggest) {
        biggest = array[i];
      }
    }
    return biggest;
  } else {
    return NaN;
  }
}
let myArray = [undefined, 8, 74, -22, 269.64, 92];

console.log(biggestNumOfArray(myArray));

answered Jun 30 '23 at 18:16

Mahadev Mirasdar

466
5
7

Bad assumption that all the numbers in my array are bigger than 0. You can put -Infinity there instead. Thanks for the answer, but i decided to just initially set biggest to -Infinity anyway. – danik0011 Jun 30 '23 at 18:21

score 0 · Accepted Answer · answered Jun 30 '23 at 18:23

@GabrielePetrioli suggested to initially set biggest to -Infinity, which worked. Thanks.

I also got took an idea from @nina-scholz to output NaN if biggest isn't a number in the end.

Here is the final fixed and working code:

const biggestNumOfArray = (array) => {
  if(Array.isArray(array)){
    let biggest = -Infinity;
    for(i=0;i<array.length;i++) {
      if(array[i] > biggest) {
          biggest = array[i];
      }
    }
    return typeof(biggest) === 'number' ? biggest : NaN;
  } else { return NaN; }
}

JS Function for seeking the biggest number in array fails when the first element is undefined or NaN

4 Answers4