Sum of all numbers in range in JavaScript

sumAllRange.js

const sumAll = (arr) => {
  // get our largest and smallest int's
  const max = Math.max.apply(null, arr);
  const min = Math.min.apply(null, arr);
  
  // how many slots are there to add?
  const slots = (max - min) + 1;
  
  // create sparse array with number of slots found
  const sumArr = Array(slots);
  
  // set an initial counter to fill the array with (increments inside `for` loop)
  let counter = min - 1; // i.e. 22 to make incrementing easy inside the `for` loop

  // fill sparse array
  for (let i = 0; i < sumArr.length; i += 1) {
    sumArr[i] = counter += 1;
  }
  
  // add the current number in the array to the previous result. We begin with 0.
  const sumOfAll = sumArr.reduce((acc, next) => {
    return acc + next;
  }, 0);
  
  return sumOfAll;
}

// example usage
sumAll([23, 46]);