Arrays

# Javascript Arrays
            ## Nerds start counting at `0`
            ---

### Terminology
            <dl>
              <dt>Array index</dt>
              <dd>The location of an item in an array. This is always a sequential number starting at <code>0</code>.</dd>
              <dt>Array item</dt>
              <dd>Any Javascript data type (i.e. value) that an array index points to.</dd>
              <dt>Array length</dt>
              <dd>The number of items in an array accessed by <code>array.length</code>.</dd>
            </dl>

---

### Value data types
            The _value_ of an item can be any data type: `undefined`, `null`, `number`, `string`, `boolean`, `array`, `object`, etc.
  
            ```js
  
            const randomStuff = [null, 9, 'Hello World!'];
            
            
            ```
  
            Although it's possible, you won't often see a mix of different value types in the same array.
  
            ---
  
            ### Accessing array items
  
            ```js
            const animals = ['Puppy', 'Bear', 'Moose', 'Tiger', 'Husky'];
            ```
            - The _first_ index of an array is `0`.
  
                ```js
                const firstAnimal = animals[0]; // Puppy
                ```
  
            - The _last_ index is `Array.length - 1`.
  
                ```js
                const lastAnimal = animals[animals.length - 1]; // Husky
                ```
            - Add an item with `array.length`.
  
                ```js
                animals[animals.length] = 'Wolf'; // New item
                ```
            
            ---
  
            ### Mutation and `const`
            Creating an array using `const` still allows you to change (or mutate) the items in that array.
  
            ```js
            const hobbies = ['pinball', 'bug hunting', 'napping'];
  
            hobbies[2] = 'proper sleeping'; // No error!
            ```
  
            `const` only stops you from _re-assigning_ `hobbies`, not changing `hobbies`.
  
            ---
  
            ## Common array methods
            
            ---
  
            ### Finding and removing items
  
            ```js
            const animals = ['Puppy', 'Bear', 'Moose', 'Tiger', 'Husky'];
  
            console.log(animals.length); // 5
  
            ```
  
            - Find the index of an item
                ```js
                let pos = animals.indexOf('Bear'); // 1
                ```
  
            - Remove an item by index position

```js
                let removedItem = animals.splice(pos, 1); 
                
                console.log(removedItem);
                // 'Bear'

console.log(animals)
                // ['Puppy', 'Moose', 'Tiger', 'Husky']
                ```
            
            ---
  
            ### Searching Arrays
            The `includes()` method determines whether an array includes a certain value among its entries, returning true or false as appropriate.
            ```js

const pets = ['cat', 'dog', 'bat'];
  
            console.log(pets.includes('cat')); // true
  
            console.log(pets.includes('at')); // false
  
            ```
  
            ---
  
            ### Converting an Array to a String
            The `join()` method creates and returns a new string by concatenating all of the elements in an array, separated by commas or a specified separator string.
            ```js
            const elements = ['Fire', 'Air', 'Water'];

console.log(elements.join()); // "Fire,Air,Water"
            
            console.log(elements.join('')); // "FireAirWater"
            
            console.log(elements.join('-')); // "Fire-Air-Water"

```

---

## Further resources
            - MDN: [Arrays](https://developer.mozilla.org/en-US/docs/Learn/JavaScript/First_steps/Arrays)
            - In [JavaScript Tutorial for Beginners: Learn JavaScript in 1 Hour](https://www.youtube.com/watch?v=W6NZfCO5SIk) by Mosh
                - 35:22 [Arrays](https://www.youtube.com/watch?v=W6NZfCO5SIk&t=2122s)
            - [Start of Array Exercises](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/basic-javascript/store-multiple-values-in-one-variable-using-javascript-arrays) on Free Code Camp