Exercism-JS/elyses-analytic-enchantments

Elyses Analytic Enchantments

Welcome to Elyses Analytic Enchantments on Exercism's JavaScript Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

Arrays have built-in methods to analyse the contents of the array. Most of these methods take a function that returns true or false as an argument. Such a function is called a predicate.

The built-in methods are meant to be used instead of a for loop or the built-in forEach method:

Example of analysis using a for loop :

const numbers = [1, 'two', 3, 'four'];
for (var i = 0; i < numbers.length; i++) {
  if (numbers[i] === 'two') {
    return i;
  }
}
// => 1

Example of analysis using a built-in method:

const numbers = [1, 'two', 3, 'four'];
numbers.indexOf('two');
// => 1

Some other helpful built-in methods that are available to analyze an array are shown below. See MDN for a full list of array methods.

includes

The includes() method determines whether an array includes a certain value among its entries, returning true or false as appropriate. ¹

const numbers = [1, 'two', 3, 'four'];
numbers.includes(1);
// => true
numbers.includes('one');
// => false

every

The every() method tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value. ²

const numbers = [1, 3, 5, 7, 9];
numbers.every((num) => num % 2 !== 0);
// => true

some

The some() method tests whether at least one element in the array passes the test implemented by the provided function. ³

const numbers = [1, 3, 5, 7, 9];
numbers.some((num) => num % 2 !== 0);
// => true

find

The find() method returns the value of the first element in the provided array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned. ⁴

const numbers = [1, 3, 5, 7, 9];
numbers.find((num) => num < 5);
// => 1

findIndex

The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise, it returns -1, indicating that no element passed the test. ⁵

const numbers = [1, 3, 5, 7, 9];
numbers.findIndex((num) => num > 7);
// => 4
numbers.findIndex((num) => num > 9);
// => -1

Instructions

Elyse, magician-to-be, continues her training. She will be given several stacks of cards that she needs to perform her tricks. To make things a bit easier, she only uses the cards 1 to 10.

In this exercise, use built-in methods to analyse the contents of an array.

1. Find the position of a card

Elyse wants to know the position (index) of a card in the stack.

const card = 2;
getCardPosition([9, 7, 3, 2], card);
// => 3

2. Determine if a card is present

Elyse wants to determine if a card is present in the stack -- in other words, if the stack contains a specific number.

const card = 3;
doesStackIncludeCard([2, 3, 4, 5], card);
// => true

3. Determine if each card is even

Elyse wants to know if every card is even -- in other words, if each number in the stack is an even number.

isEachCardEven([2, 4, 6, 7]);
// => false

4. Check if the stack contains an odd-value card

Elyse wants to know if there is an odd number in the stack.

doesStackIncludeOddCard([3, 2, 6, 4, 8]);
// => true

5. Get the first odd card from the stack

Elyse wants to know the value of the first card that is odd.

getFirstOddCard([4, 2, 8, 7, 9]);
// => 7

6. Determine the position of the first card that is even

Elyse wants to know the position of the first card that is even.

getFirstEvenCardPosition([5, 2, 3, 1]);
// => 1

Source

Created by

• @peterchu999
• @SleeplessByte

Contributed to by

• @pertrai1

---

1. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes ↩︎

2. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every ↩︎

3. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some ↩︎

4. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find ↩︎

5. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex ↩︎