public/subjects/reduce.en.md

Reduce

Instructions

Create three functions:

• fold that receives an array, a function and an accumulator, in this order, and applies the function in the elements of the array starting on the left.

• foldRight that receives an array, a function and an accumulator, in this order, and applies the function in the elements of the array starting on the right.

• reduce that works just like the method [].reduce when you don't specify an accumulator. The arguments should be an array and a function. The starting value of your accumulator must be the first value of the array. If your array is less than 1 argument you should throw an error.

• reduceRight like reduce, from the last value to the first

Example:

const adder = (a,b) => a + b
fold([1,2,3], adder, 2) // returns 8 (2 + 1 + 2 + 3)
foldRight([1,2,3], adder, 2) // returns 8 (2 + 3 + 2 + 1)
reduce([1,2,3], adder) // returns 6 (1 + 2 + 3)

The use of [].reduce and [].reduceRight is forbidden for this exercise.

Notions

• https://devdocs.io/javascript/global_objects/array/reduce

Code provided

Array.prototype.reduce = undefined
Array.prototype.reduceRight = undefined