hwk-arr-methods.md

Homework Tasks

Map

Your function must use map method

• Write a function which returns array of usernames.

  const users = [
    {
      username: "Yuri Gagarin",
      lang: "ru",
    },
    {
      username: "Nil Armstrong",
      lang: "ENG",
    },
  ];
  getUserNames(users); // ['Yuri Gagarin', 'Nil Armstrong']

• Write a function which returns array of lengths of user names

  const users = [
    {
      username: "Yuri Gagarin",
      lang: "ru",
    },
    {
      username: "Nil Armstrong",
      lang: "ENG",
    },
  ];
  getUsernameLengths(users); // [12, 13]

  • Write a function which parses string integers. If it's not possible to parse, then add null

  parseInteger(["1", "2", "34"]); // [1, 2, 34];
  parseInteger(["1", "px", "2323"]); // [1, null, 2323];

Filter

Your functions must use filter method

• Write a function which remove users with language equals to 'ru'.

  const users = [
    {
      username: "Yuri Gagarin",
      lang: "ru",
    },
    {
      username: "Nil Armstrong",
      lang: "ENG",
    },
  ];
  filterUsers(users); // [{ username: "Nil Armstrong, lang: "ENG" }]

  • Write a function which filters object by field.

  const users = [
    {
      username: "Yuri Gagarin",
      lang: "ru",
      isAstronaut: true,
    },
    {
      username: "Nil Armstrong",
      lang: "ENG",
      isAstronaut: true,
    },
    {
      username: "Elon Musk",
      isAstronaut: false,
    },
  ];
  filterByField(users, "isAstronaut"); // [{ username: "Yuri Gagarin", lang: "ru", isAstronaut: true, }, { username: "Nil Armstrong, lang: "ENG" }]

Reduce

Your function must use reduce

• Write a function which calculates average age of users.

  const users = [
    {
      username: "Yuri Gagarin",
      lang: "ru",
      age: 56,
    },
    {
      username: "Nil Armstrong",
      lang: "ENG",
      age: 54,
    },
  ];
  getAverageAge(users); // 55

Methods

• *Implement these array methods
  • forEach
  • filter
  • map
  • every, once