In Javascript, given a simple number[] array, is there an elegant way to calculate the minimum and maximum values simultaneously, or return undefined if the array is empty?

Something like this:

const a = [1, 2, 3];
const (min, max) = minMax(a);

Pre-emptive response notes:

1. This is not a duplicate of this question because he is not actually calculating the min and max of the same array, but the min or max of 4 different arrays.

2. I want to calculate these in one pass. Not [Math.min(a), Math.max(a)].

3. I know how to do the obvious way:

let min = undefined;
let max = undefined;
for (const x of array) {
  min = min === undefined ? x : Math.min(min, x);
  max = max === undefined ? x : Math.max(max, x);
}

I am wondering if there is something a bit more elegant, e.g. using Array.reduce().

In Javascript, given a simple number[] array, is there an elegant way to calculate the minimum and maximum values simultaneously, or return undefined if the array is empty?

Something like this:

const a = [1, 2, 3];
const (min, max) = minMax(a);

Pre-emptive response notes:

1. This is not a duplicate of this question because he is not actually calculating the min and max of the same array, but the min or max of 4 different arrays.

2. I want to calculate these in one pass. Not [Math.min(a), Math.max(a)].

3. I know how to do the obvious way:

let min = undefined;
let max = undefined;
for (const x of array) {
  min = min === undefined ? x : Math.min(min, x);
  max = max === undefined ? x : Math.max(max, x);
}

I am wondering if there is something a bit more elegant, e.g. using Array.reduce().

• javascript
• arrays
• numbers
• max
• min

• there is no Math.reduce function, do you mean Array.reduce? And if so, just put your for of loop in the reduce function and you're done. – pretzelhammer Commented Jun 24, 2020 at 13:58
• Ah yeah oops, thanks! And it isn't as simple as that because the input and output of reduce have to be the same type. I could do array.map(x => [x, x]).reduce(...) but euurgh. Not my idea of elegant. – Timmmm Commented Jun 24, 2020 at 14:00
• array.reduce(([min,max], x)=>[Math.min(min,x),Math.max(max,x)],[,,].fill(array[0]))? – user120242 Commented Jun 24, 2020 at 14:09

4 Answers 4

You can use Array.reduce() to reduce into any kind of result, it doesn't have to be the same type. For example, reducing an array of numbers into an output array of two numbers, min and max:

const minMax = arr => 
  arr.reduce(([min,max=min],num) => [Math.min(num,min),Math.max(num,max)], arr);

const a = [5,2,6,3,3,1,1];
const [min,max] = minMax(a);

console.log("min",min,"max",max);

The reduce is seeded with the array itself, for brevity and because anything else is somewhat unnecessary. This would mess up arrays of length 1 due to the destructuring, so max=min is used to set max equal to the first element as a fallback. So cases of array length 1 or 0 are handled.

Using Array.reduce and only iterating over the array once. I'm using array destructing assignment to pass back both min and max values from the function (since JS doesn't have tuple types). I'm also checking for the edge cases of the array being empty:

function minMax(array) {
  if (array.length == 0) {
    return [undefined, undefined];
  }
  return array.reduce(([min, max], val) => {
    return [Math.min(min, val), Math.max(max, val)];
  }, [Number.MAX_VALUE, Number.MIN_VALUE]);
}

function testMinMax(array) {
  let [min, max] = minMax(array);
  console.log(min, max);
}

testMinMax([]); // logs "undefined undefined"
testMinMax([1]); // logs "1 1"
testMinMax([1, 2, 3, 4, 5]); // logs "1 5"

With spread operator bining with Math.min and Math.max

const a = [1, 2, 3];

const [min, max] = [Math.min(...a), Math.max(...a)];

console.log({min, max});

Why not just this:

function minMax(arr) {
    arr = arr.sort((a, b) => a - b);
    return [arr.at(0), arr.at(-1)]
}
const a = [1, 2, 3];
const [ min, max ] = minMax(a);