JavaScript Array Reduce from Scratch

javascriptArrayReduceFromScratch.js

// 1 - Create reduce function
function reduce(arr, fn, acc){

  // 5 - Iterate over each array value and reduce it with the accumulator into only one, assigning the result to the accumulator
  for(value of arr){
    acc = fn(value, acc);
  }
  
  // 6 - Return the accumulator after iterates over each value of the array
  return acc;
}

// 2 - Create an array to iterate into reduce
const myArr = [1,2,3];

/ 3 - The callback function to reduce each array value and the accumulator into one
function add(a, b){
  return a + b;
}

// 4 - Execute the reduce function with myArr, add function and return it to countFullArray const
const countFullArray = reduce(myArr, add, 0); // 6