iKnowJavaScript

// one liner
const sum = (arr) => arr.reduce((acc, item) => acc + item, 0);

const doubleNumber = (arr) => arr.map((item) =>item * 2)

//dont forget to export 
module.exports = { sum, doubleNumber }

iKnowJavaScript

// reguire the real file to be tested
const { sum, doubleNumber} = require("./logic.js") //use correct path

describe("Sum function should return the sum of all the numbers in an array", function() {
  it("Should return 4 for [1,2,1]", function() {
    expect(sum([1,2,1])).toEqual(4)
  })
  it("Should return 10 for [1,2,3,4,5]", function() {
    expect(sum([1,2,3,4,5])).toEqual(15)
  })

iKnowJavaScript

function sum(arr) {
  let total = 0;
  for(let i = 0; i < arr.length; i++) {
    total += arr[i];
  }
  return total;
}

const numbers = [1,2,3,4,5]
sum(numbers); //15

iKnowJavaScript

function Admin(name, email) {
  User.call(this, name, email);
  this.isAdmin = true;
}

Admin.prototype = Object.create(User.prototype);
Admin.prototype.constructor = Admin;

// we can now add methods and props to Admin Prototype
Admin.prototype.deleteAllComment = function() {

iKnowJavaScript

// User constructor
function User(name, email) {
  this.name = name;
  this.email = email;
  this.isAdmin = false;
}

// We can now add methods to its prototype like so...
User.prototype.postComment = function(message) {
    //add Post implementation here

iKnowJavaScript

// User constructor
function User(name, email) {
  this.name = name;
  this.email = email;
  this.isAdmin = false;
}
// Note: this "{}" represent the Constructor itself