Imperative and OOP vs. functional programming code example

example.js

// OOP anad imperative example

class Todo {
  constructor(action, assignee) {
    this.action = action
    this.assignee = assignee
    this.complete = false
  }

  toggleComplete() {
    this.complete = !this.complete
  }
}

class TodoList {
  constructor(...todos) {
    this.todos = [...todos]
  }

  assignAllTo(assignee) {
    for (let i = 0; i < this.todos.length; i++) {
      this.todos[i].assignee = assignee
    }
  }

  completeAll() {
    for (let i = 0; i < this.todos.length; i++) {
      this.todos[i].toggleComplete()
    }
  }
}

// Make a few new todo items
let firstTodo = new Todo("hypnotize some people", "Will")
let secondTodo = new Todo("get bored", "Will")

// Create the list and reassign
let willsList = new TodoList(firstTodo, secondTodo)
// willsList.todos = [Todo("hypnotize some people", "Will", false), Todo("get bored", "Will", false)]
list.assignAllTo("Dad")
list.completeAll()
// willsList.todos = [Todo("hypnotize some people", "Dad", true), Todo("get bored", "Dad", true)]

// ------------------------------------------------------------------------------

// Functional example
function assignAllTo(todos, assignee) {
  return todos.map((todo) => {
    return {assignee: assignee, ...todo}
  })
}

function completeAll(todos) {
  return todos.map((todo) => {
    return {complete: true, ...todo}
  })
}

const firstTodo = {action: "hypnotize some people", assignee: "Will", complete: false}
const secondTodo = {action: "get bored", assignee: "Will", complete: false}
const willsList = [firstTodo, secondTodo]
const dadsList = completeAll(assignAllTo(willsList, "Dad"))
// dadsList = [{action: "hypnotize some people", assignee: "Dad", complete: true}, {action: "get bored", assignee: "Dad", complete: true}]
// willsList = [{action: "hypnotize some people", assignee: "Will", complete: false}, {action: "get bored", assignee: "Will", complete: false}]