Array method exercises

Task 1 - various

1. Install dependencies with yarn
2. Run yarn test to check that jest runs the tests but they fail for sensible reasons
3. Consult the tests and edit myFunctions.js
4. implement the functions in myFunctions.js until all tests pass.

Task 2 - map practice

1. Follow the setup steps as per task 1 if you have not already done so
2. run yarn test mapPractice to only run the tests for this task
3. Consult the tests in mapPractice.test.js
4. and edit the functions in mapPractice.js
5. implement the functions until all tests pass.

You should use the array.map function in your solution for each of these functions.

Conveniences

Run tests on every change

By adding --watch to an instruction to jest, you can cause tests to be re-run every time a relevant file is changed. E.g.

yarn test mapPractice --watch

Run only one test

Note that you can amend a test to be the only one to run, when you want to focus on it, as follows:

    test.only("square all numbers"

instead of

    test("square all numbers"

Rules:

Rule: No explicit loops

Weirdly, your code should not contain any loop structures (no for or while loops).

Rule: use the built-in array methods

Unlike in some earlier katas, for this set of exercises you should try to make use of some of the built-in js array methods instead.

Specifically, you should research the following, to see which ones can help you. (You won't need them all.)

• array.find
• array.findLast
• array.findIndex
• array.filter
• array.some
• array.includes
• array.indexOf
• array.every
• array.map

Extra clarifications

• It's fine to make little helper functions to get the work done
• It's fine to use arrow functions or normal function declaration syntax wherever you like, except...
• Don't change the signature (first line) of the given functions, nor their jsdoc, only their bodies.
  • (so, also don't change the form of the existing functions to be arrow functions.)
• It should not be necessary to edit the test file. (though you are welcome to add MORE tests to give further clarity or visibility into any problem)