JavaScript® (often shortened to JS) is a lightweight, interpreted, object-oriented language with first-class functions, most known as the scripting language for Web pages, but used in many non-browser environments as well such as node.js or Apache CouchDB. It is a prototype-based, multi-paradigm scripting language that is dynamic, and supports object-oriented, imperative, and functional programming styles.

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Learn Javascript

Wouldn't it be nice if everyone ran the tests before committing code? With ghooks, you can automatically add a githook when dependencies are installed which will allow you to define common scripts to be run at various points during git actions (like committing). In this lesson, we'll add a githook for running the tests before we commit code to make sure we don't commit anything that breaks the tests.

Automatically running tests before commits with ghooks

Regular Expression Word Boundaries allow to perform "whole word only" searches within our source string.

Find the Start and End of Words with Regular Expression Word Boundaries

React is one of the web’s most popular frameworks for building JavaScript applications. 

If you know what you’re doing, React can drastically simplify how you build, use, and maintain code.

Whether you’re a React newbie or you’re ready for advanced techniques, you can level-up with egghead. Explore our in-depth courses, lessons, and community resources to build more powerful applications and crack open your career.

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Sometimes you need to cancel a pending request based on an action performed by the User. In this lesson we’ll see how we can stop an in-flight ajax request by dispatching another action into the store and making use of the Rx operator ‘takeUntil’.

Use an action to cancel an Ajax request

This lesson will utilize the Istanbul tool to instrument our code for code coverage recording and reporting. We'll use this to make sure that as our library gets new features, we keep track of our coverage and can find places to improve it.

Adding code coverage recording with Istanbul

Javascript modules are a great way to isolate your code, but they are not very re-usable.  If we implement the factory pattern inside of one of our modules we get code re-use without losing the encapsulation benefits of a javascript module.

The Factory Pattern for Javascript Modules

Now that we're keeping track of our coverage, let's upload our reports to a third party service so we can track our stats over time. In this lesson we'll show how easy it is to upload our stats to codecov.io.

Add code coverage reporting

Speed up your Sublime Text workflow by creating snippets out of boilerplate code. Sublime Text snippets are smart, configurable, and prevent repetitive typing.

Use Sublime Text Snippets to Avoid Repetitive Typing

Writing the code in the next version of JavaScript can really simplify the development of a library. In this lesson, learn how to create a build which uses the BabelJS transpiler to enable you to write your code using ES6 (aka ES2015) syntax.

Adding ES6 Support

Learn a few advanced reduction patterns: flatten allows you to merge a set of arrays into a single array, the dreaded flatmap allows you to convert an array of objects into an array of arrays which then get flattened, and reduceRight allows you to invert the order in which your reducer is applied to your input values.

Learn to Flatten and Flatmap Arrays with Reduce

By adding ES6 support to our source code, we need to add that same support to our tests so we can consume that synatx. This is quite easy with the `--compilers` flag for `Mocha`.

Adding ES6 Support to Tests using Mocha and Babel

In this lesson, we will be looking at two common mistakes programmers make when working with `reduce.` We will see why we always need to pass in an initial value for our accumulator as well as return the accumulator.

Avoid Common Mistakes when Working with Reduce

Let's take a closer look at using Javascript's built in Array reduce function. Reduce is deceptively simple and when harnessed correctly can achieve very powerful results. By leveraging reduce, we can answer a variety of questions on a single, simple data set. In this lesson, we'll look at how you might use [Array.prototype.reduce](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce) to:

- Sum an array of numbers
- Reduce an array of objects to a sum of a given property
- Group an array of objects by key or a set of given criteria
- Count the number of objects in an array by key or a given set of criteria

Array.prototype.reduce in JavaScript by example

Javascript has first-class functions which means that any function can stored, passed around, and returned just like an Object can. This allows for a lot of flexibility with how you call functions. This allows us to use array reduction to create functional pipelines by composing arrays of functions.

Compose Functions with Reduce

We examine the data structure Task, see some constructors, familiar methods, and finally how it captures side effects through laziness.

Capture Side Effects in a Task

Chaining operations like `map` and `filter` on an array can have performance issues as we have to iterate through the whole array for every operation.

In this lesson we explore this problem by doing some basic array transformations and measuring their performance.

 We’ve got two utility function to help us with this:
* `arrayOfRandoms` is a higher order function which helps us create a range of random numbers
* `timeIt` will help us measure how long functions take to execute

It's important to understand this problem and why it occurs before we move on to how transducers handle it differently.

Understand why Transducers can Improve Performance

`JSON` (JavaScript Object Notation) is a standard method to serialize JavaScript objects and is commonly used to transfer data from the server to the browser. The browser has a `JSON` API that allows you to parse the `JSON` string into a JavaScript object. This API allows you to customize the parsing behavior very specifically as well.

The JSON.parse API

In this lesson, you will learn the difference between the exports statement and module.exports. Two examples are demonstrated, each accomplishing the same task but one using export statements and one using module.exports. You will also learn the basic thumb rule to identify which is appropriate for your current needs.

Export Modules in Node.js

In this lesson, we introduce modules: what they are and how to use them. You'll learn:
how to create a simple module and export the functions to be accessed elsewhere
how to include code from your module in files within your application
the three rules node uses to find the modules you require
the hierarchy node uses to determine which modules take precedence
which file extensions node can automatically detect when requiring modules

Create a Simple Node.js Module

We use an offset exporting function to get the address of a string in WebAssembly memory. We then create a typed array on top of the WebAssembly memory representing the raw string data, and decode that into a JavaScript string.

WASM Fiddle: https://wasdk.github.io/WasmFiddle/?6wzgh

Demo Repo: https://github.com/guybedford/wasm-intro

Read WebAssembly Memory from JavaScript

It is some times convenient, even necessary, to make use of a module that you are working on before it has been published to the node package manager (npm). The `npm link` command makes this simple.

Using npm link to use node modules that are "in progress"

An introduction to the Web Audio API. In this lesson, we cover creating an audio context and an oscillator node that actually plays a sound in the browser, and different ways to alter that sound.

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