We will learn what arrays are and what their purpose is in our programs and lives.

A lecture explaining what references are. As many values in arrays are stored as references, it pays to understand this concept.

To better understand arrays, we look at some concepts that are closely tied to the idea of arrays.

In this video, we take a look at unique properties of JavaScript arrays that do not exist in all other programming languages.

We look at some of the differences between JavaScript arrays and JavaScript objects.

Let's quickly review what we've learned in this chapter

In this video, we will learn how to access elements in arrays we have created.

Now that we can create arrays, we will learn how to add new elements to them.

In this video, we will learn how to change elements of arrays without affecting the others.

Though it is not a best practice, strings can be used as indexes as well as integers. We will learn about this phenomenon in this video.

One of the more challenging elements of JavaScript arrays is removing elements from them. This video will explore a few way of doing so.

We will wrap up what we've learned in this chapter.

See the attached PDF for a bonus reference on arrays.

We'll have a look at what this chapter will include.

•  Performing the same action on some or every element of the array is called iteration
•  Taking an array and turning it into a single value is called reduction
•  We will cover every built in way to iterate over arrays including…
  •  Maps
  •  Filters
  •  For Each
•  We will cover many ways to reduce arrays including…
  •  Reduce
  •  Every

Explanation of the usefulness of iteration.

•  Arrays often contain large amounts of information, from which it can be difficult to discern meaning
•  Arrays can contain a variety of elements, some of which are not useful for what you need to do
•  The elements in an array can be in incorrect, or inconsistent, form
•  Array elements can be in the wrong order

An explanation, and demonstration, of For Loops.

•  For Loops are basic loops that are flexible but can be difficult to understand and verbose to write

•  Called for loop because it uses the “for” keyword, and loops through all the elements of an array

•  For loops can be used for any operation that needs to occur a set number of times, not just array

In this video we discuss For Each Loops.

• Very similar to For Loops  but ony work for arrays
• Less flexible and less useful for other purposes, but perfect for arrays
• A function will run once for each element of the array, and will be passed arguments corresponding to each element and its index

Demonstration and discussion of the consequences of modifying arrays during loops.

•  Removing array elements while iterating over them can cause very confusing results
•  This operation throws an error in many other languages but not JavaScript
•  As a general rule, do not remove elements from arrays while iterating over them, use filters instead (see later video)
•  Possible (but confusing) solution is to use backwards for loop

We discuss and have a look at While Loops, another way to loop through arrays.

• Most brief loop to write
• While loops can easily crash Chrome or a Node server
• Can be difficult to understand or “grok”
• Not recommended for use outside of recreational coding challenges

A demonstration and explanation of array filters, a very useful array method.

• Used to weed out unwanted array elements
• An array filter is a safe way to remove multiple elements from an array at once
• Creates a copy of the original array with equal or fewer elements (original array is not changed)

Video and demonstration of array maps.

•  Used to transform each element of an array in the same way
•  Can turn an array of objects into an array of strings
•  Like filter, creates a copy
•  Maps always have the same number of elements in them as the original

Explanation and demo of array reduction, or folding.

•  Reducing an array means taking all the values of an array to a single value
•  A simple example is to reduce an array of numbers to the sum of all those numbers
•  Reductions are very useful as they crystalize (sometimes thousands) of pieces of data into just one number or Boolean or string, etc.

We look at some built-in filters including every, some and find.

• Turns an entire array into a single true or false value
• The function passed to every or some which determines if an array element passes is called a predicate
• .every() only returns true if the predicate is true for every element
• .some() returns true if the predicate is true for one or more element

A brief word on Array Includes.

•  Returns true if any element of the array matches the value that is passe

A demo and explanation of chaining array methods, a useful feature of JavaScript.

• Chaining array methods together can create complex operations like reductions or map-filters
• JavaScript is one of the best existing langauges for chaining array methods
• Recommended method for processing large amounts of data

We conclude what we have learned in this chapter.

• It is often necessary to reduce arrays to just one value – use a reduction for that
• While loops are dangerous to use,and removing elements from an array while looping through it is also not recommended
• JavaScript has a rich variety of built in map, filter and reduction functions
• Map, filter, includes, some, every and reduce are most useful built in features
• Knowledge can be applied directly to front-end code or database code on a Node.js platfor

•  Changing the order of some or all of the elements of an array, without changing of them, is called sorting
•  We will cover all built-in sorting methods
•  We will also look at sorting available from external libraries in a later chapter

An explanation of the uses of array sorting.

• Sometimes arrays of elements are not in the order desired
• Some operations, like converting elements of an array into text posts and appending them to a document, have different results based on the order of arrays
• Other operations, like finding the sum of an array, are not affected by order at all

An explanation and demonstration of sorting arrays.

• The built-in array sort method can take a function as an argument
• The function always takes two arguments, a and b, representing any two potential elements of the array
• If a number less than 0 is returned, then a should have a lower index than b in the final array

We conclude the chapter.

• Sorting arrays is necessary for many practical applications
• The built in sort function should not be used without an argument as it produces unexpected results
• Using the built in sort function modifies the original array

In this video we look ahead at this chapter, and explain and demonstrate the Spread operator.

•  Expands an array
•  Convenient shorthand
•  Takes an array and spreads it out into all its elements
•  Only works while defining arrays

Next, we look at the Rest Operator, the cousin of the Spread Operator. Includes demo.

•  Takes all the arguments supplied to a function and turns them into an array
•  Useful for functions where large amount of arguments are passed to it
•  Only works inside the arguments section of a function declaration

We review what we learned in this chapter

• It is not necessary to use Rest and Spread but usually it is clearer if they are used
• Only work in ES6-compatible environments

We'll take an overview of this chapter on libraries.

• JavaScript has useful, but few, built-in array functions
• Writing one’s own functions for simple things like sum, product, max, etc. is time-consuming
• Libraries have been written to help manipulate arrays

This video provides an explanation and demonstration of the array manipulation library Lodash.

• Underscore older; Lodash newer, fresher, better tested
• Full of utility functions for operating on arrays

In this video we look at and demo D3.js

• D3’s primary purpose is to display data visually using DOM elements
• It is also packed with loads of helper functions for working with 

We review what we learned about array manipulation libraries in this chapter.

• D3 and Underscore have more than 50 functions to work with arrays
• Only way to master these libraries is to practice with them

In this final lecture, we review all the things we covered in previous chapters.

We have a look at some continued education resources to keep learning after the completion of this course. (See resources)

A special thank you video to congratulate you on successfully completing this course.