JS - Sum Of Two Arrays where arrays can be of unequal length

Question

I need function like this.

function sum(arr1, arr2) {
  return totalArray
};

sum([1,2,3,4], [5,6,7,8,9]) // [6,8,10,12,9]

I tried it this way:

var array1 = [1, 2, 3, 4];
var array2 = [5, 6, 7, 8, 100];
var sum = array1.map((num, idx) => num + array2[idx]); // [6,8,10,12]

Answer 1

First you can get an array out of the function's arguments using Spread syntax (...), then sort it by array's length using Array.prototype.sort() and finally Array.prototype.reduce() to get the result array

Code:

const sum =(...arrays) => arrays
  .sort((a, b) => b.length - a.length)
  .reduce((a, c) => a.map((n, i) => n + (c[i] || 0)) || c)

// two arrays
const resultTwoArrays = sum([1, 2, 3, 4], [5, 6, 7, 8, 9])
console.log(resultTwoArrays) // [6, 8, 10, 12, 9]

// three arrays or more...
const resultThreeArrays = sum([1, 2, 3, 4], [5, 6, 7, 8, 9], [1, 2])
console.log(resultThreeArrays) // [7, 10, 10, 12, 9]

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