stevenjlance / arrays-code-along

ARRAYS

Up to this point we have used variables to store information. For example, if I wanted to store my favorite foods I would need to make individual variables for each of the items.

var favFood1 = "Pizza";
var favFood2 = "Ice Cream";
var favFood3 = "Tacos";

In JavaScript, an array (the general term is list) is a special variable, which can hold more than one value at a time. For example, I could make an array of my favorite foods and store them in a single variable.

var favFood = ["Pizza", "Ice Cream", "Tacos"];

CRUD (Create, Read, Update, Delete) Array Operations

As with everything we have learned in this class, you should utilize documentation when working with arrays. When working with arrays, you should have knowledge of CRUD (Create, Read, Update, and Delete) operations for arrays.

To create a list, we simply need to use [] and seperate each value with a comma.

// Create a list
var favFood = ["Pizza", "Ice Cream", "Tacos"];

To read a list (or access a specific value), we use the index of the item. NOTE: In computer science we start by counting from 0, so the first item in a list has an index of 0, the second an index of 1, etc.

// Read a list
console.log(favFood[2]);
// Prints out a value of Tacos as tacos has an index of 2.

To update a value in an array, we use a very similar method to how we updated a variable except we now also include the index that we want to update the value for. Lets say I wanted to change Ice Cream to a new value. We can use the index of 1 to update this value

// Update a list
favFood[1] = "Chicken",
console.log(favFood)
// favFood is now equal to ["Pizza", "Chicken", "Tacos"]

Let's say we just wanted to add an item to an array. We can use .push() to push more items to a list. This will add the value to the END of the list

// Update a list
favFood.push("Chocolate");
console.log(favFood)
// favFood is now equal to ["Pizza", "Chicken", "Tacos", "Chocolate"]

Finally, we can delete a list item using the .shift() method the remove the first item in a list and the .pop() method to remove the last item in a list

// Delete the first item in a list
favFood.shift();
console.log(favFood)
// favFood is now equal to ["Chicken", "Tacos", "Chocolate"]

//Delete the first item in a list
favFood.pop();
console.log(favFood)
// favFood is now equal to ["Chicken", "Tacos"]

Suppose we wanted to delete an item in the middle of the array. We can use the .splice method to achieve this:

// Delete the one item on the list starting at an index of 2
favFood.splice(1, 1);
console.log(favFood)
// favFood is now equal to ["Chicken"]



`.length` Method
------------------
The final method that we will use with arrays is the `.length` command. The length property  returns the number of elements in an array. This is particularly useful when you have a long array and need to go through the entire array. This command will become particularly powerful when we attempt to process arrays.
```javascript
var favNumbers = [22, 8, 7, 982, 31, 538, 270];
console.log(favNumbers.length);
// Returns a value of 7 as there are 7 items in this list.