# Array

In JavaScript, an array is a special data type that is used to store a collection of elements, such as numbers, strings, or even other arrays. Each element in the array is assigned an index, which starts at 0 for the first element and increments by 1 for each subsequent element.

To create an array in JavaScript, you can use the square bracket notation like this:

```javascript
let myArray = [1, 2, 3, 4, 5];
```

This creates an array with 5 elements, each containing a number from 1 to 5. You can also create an empty array and add elements to it later like this:

```javascript
let myEmptyArray = [];
myEmptyArray.push(1);
myEmptyArray.push(2);
myEmptyArray.push(3);
```

This creates an empty array and then adds the numbers 1, 2, and 3 to it using the `.push()` method.

You can access individual elements in an array using their index, like this:

```javascript
let myArray = [1, 2, 3, 4, 5];
console.log(myArray[0]); // outputs 1
console.log(myArray[3]); // outputs 4
```

You can also modify individual elements in an array by assigning a new value to their index, like this:

```javascript
let myArray = [1, 2, 3, 4, 5];
myArray[2] = 10;
console.log(myArray); // outputs [1, 2, 10, 4, 5]
```

You can also use various built-in methods to manipulate arrays, such as `.push()` to add an element to the end of the array, `.pop()` to remove the last element from the array, `.shift()` to remove the first element from the array, and `.unshift()` to add an element to the beginning of the array.

Here are some examples of using these methods:

```javascript
let myArray = [1, 2, 3, 4, 5];
myArray.push(6); // adds 6 to the end of the array
myArray.pop(); // removes 6 from the end of the array
myArray.shift(); // removes 1 from the beginning of the array
myArray.unshift(0); // adds 0 to the beginning of the array
console.log(myArray); // outputs [0, 2, 3, 4, 5]
```

#### A basic array problem for you to practice

Write a function called `sumArray` that takes an array of numbers as an argument and returns the sum of all the numbers in the array.

Example usage:

```scss
sumArray([1, 2, 3, 4, 5]); // returns 15
sumArray([10, -5, 7, 9]); // returns 21
sumArray([]); // returns 0
```

Hint: You can use a `for` loop to iterate through the array and add up the numbers.