nativeMethods.js

// Simple implementation of [].reduce

Array.prototype.myReduce = function (reducer, initialValue) {
	let result = initialValue

  this.forEach(item => {
  	result = reducer(result, item)
  })
  
  return result
} 

// tests
console.log([1 ,2, 3, 4, 5].myReduce((acc, curr) => acc + curr, 0))
console.log([[1,2,3], 4, 5, 6].myReduce((acc, curr) => acc.concat(curr), []))