Using the reduce function to return an array

Question

Why is it that when I want to use the push function inside the reduce function to return a new array I get an error. However, when I use the concat method inside the reduce

Answer 1

Array.prototype.push method returns the new length of the array.

Array.prototype.concat method inserts new element into array and returns array back so it can be further processed. This is what you need to do with reduce: pass modified array the the next iteration.