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

The concept of 'done-ness' is not something that is often considered when writing functions in JavaScript — you end up just running out of data or a function stops getting called.

There are many async scenarios that make sense to signal that work is completed. 

By following a completion pattern, we can easily trigger repetition and sequencing (async or not) into our code.

**You're in Section 05 of [Composing Closures and Callbacks in JavaScript](https://egghead.io/playlists/composing-closures-and-callbacks-in-javascript-1223)**

After a broadcaster is "done", starting it up again requires calling the broadcaster with the same listener. This creates a kind of "async recursion" where you pass the listener back into the broadcaster each time you set it up. This lesson walks through creating a repeat operator that can start a broadcaster over.

Repeat a Broadcaster that Is Done

Apps often have scenarios where one event controls another. In operators, this requires passing one broadcaster in and using it to control another broadcaster. You can think, "when this broadcaster fires, do that with the other broadcaster". This lesson covers using one broadcaster to control when another broadcaster repeats.

Repeat When Done with a Repeat Operator

`repeatWhen` and `startWhen` both use the concept of an "outer broadcaster" controlling an "inner broadcaster". This lesson explores how the two compare and the importance of understanding their relationships and determining when they're done.

Comparing Repeat to Start

Asynchronous code often uses conditions to determine when a block of code should finish running. This lesson walks through writing a `doneIf` operator which can check the current value passed through against a custom condition and pass a `done` value if that condition is `true`.

Marking Done Based on a Condition

Many scenarios involve one task happening after another has completed. This lesson walks you through setting up "steps" which trigger one after another to create an asynchronous sequence of tasks.

Create a Sequence of Broadcasters

A sequence is often based on a series of values pre-defined in an Array. This lesson shows you how to take advantage of a buffer and the `done` values to split an Array into an asynchronous sequence of values.

## Congrats on finishing Section 05: Use a Completion Pattern to enable Repetition and Sequencing!🎉🎉

  👉  **[CLICK HERE to continue to the next section, Bringing the Pattern into React.](https://egghead.io/playlists/bringing-the-pattern-into-react-decf)** 👈 

Use a Completion Pattern to enable Repetition and Sequencing

John Lindquist

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