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.

javascript

Now that you've been introduced to the pattern in-depth, let's implement it in a few common Async Scenarios.

You'll notice the benefits of re-using broadcasters through different scenarios as well as tweaking behavior through operators like when to start and stop code.

**You're in Section 04 of [Composing Closures and Callbacks in JavaScript](https://egghead.io/playlists/composing-closures-and-callbacks-in-javascript-1223)**

We've written a lot of code up to this point, but let's take a step back and try a demo from scratch to help see the pattern evolve. This lesson walks through creating a counter demo which can add a number when you click an add button or subtract number when you click a subtract button. 

Count the number of reusable function that were created in this lesson compared to writing this with nested callbacks

Building a Counter UI by Composing Callbacks

Controlling when a broadcaster starts and stops gives you complete control over your broadcasters. This let's you hook multiple pieces of UI together to offer to the user and allow them to manage the behaviors of your application. This lesson walks through creating a timer using a startWhen and a stopWhen operator which are hooked into buttons. 

Think of some other scenarios where have beginnings and ends controlled by events. For example, a mouse drag that starts with a mouse down and ends with a mouse up

Building a Timer UI by Composing Callbacks

It's common for a user to enter values that you want to check against your pre-defined values. Let's make a demo of a word game to demonstrate one approach to solving that use case.

Try consolidating map(hangmanLogic) even further into a stand-alone hangmanLogic operator so that there's no mapping, just the hangmanLogic operator

Building a Word Matching Game by Composing Callbacks

Many streams of events end when a certain condition is met. When we run into that condition, we'll want to pass down our own custom values. This lessons walks through adding a done condition to hangman and how we can use new operators to control what happens when it's done.

## Congrats on finishing Section 04: Implement the Pattern in Common Async Scenarios!🎉🎉

  👉  **[CLICK HERE to continue to the next section, Use a Completion Pattern to enable Repetition and Sequencing.](https://egghead.io/playlists/use-a-completion-pattern-to-enable-repetition-and-sequencing-f0ba)** 👈 

Implement the Pattern in Common Async Scenarios

John Lindquist

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