reduce() method

How to use reduce() method

by Frank Liu

JavaScript

const arr = [1,2,3,4,5];

const sum = (prev, cur, index, arr)=>{
	console.log("index = ",index);
  console.log("array is : ", arr);
	const res = prev + cur;
  return res;
}

const result = arr.reduce(sum);
console.log("The calculation result: ", result);
// Give an initial value for the reducer
console.log("The calculation result: ", arr.reduce(sum,100));

// reduceRight();
console.log("The reduceRight() calculation result: ", arr.reduceRight(sum));