Скачать или смотреть Mastering Observable Streams: Running a Repeating Function Every 500ms in RXJS

Learn how to leverage RXJS Observables to execute a function repeatedly every 500ms, filtering results to output only specific data.
---
This video is based on the question https://stackoverflow.com/q/66481840/ asked by the user 'MrYutz' ( https://stackoverflow.com/u/2342450/ ) and on the answer https://stackoverflow.com/a/66483123/ provided by the user 'Steve Holgado' ( https://stackoverflow.com/u/7838401/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: RXJS Observables - Run a repeating function every 500ms and output results to an observable stream

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Mastering Observable Streams: Running a Repeating Function Every 500ms in RXJS

As a developer new to RXJS and Observables, you may encounter situations where you need to execute a repeating function at specified intervals. A common requirement is to call a function every 500 milliseconds, process the results, and send filtered data through an observable stream. In this guide, we will explore a solution to achieve just that, using an example that will help you understand the concept more clearly.

The Problem

Imagine you are working with a chart that has various shapes, and your aim is to retrieve the positions of all horizontal lines in the chart every 500 milliseconds. The steps you want to achieve include:

Call a function every 500 milliseconds to get shapes from the chart.

Filter the returned array to focus only on horizontal lines.

Output only this filtered data as an observable stream.

The Challenge

While you may have some code that seems functional, it might not be operating as desired due to the lack of repetition. Understanding how to use timers, delays, or intervals with RXJS 6 can be tricky for newcomers — but fret not; we’ll break it down step by step!

The Solution

To create a repeating function that emits results every 500ms, you will need to ensure that your observable completes after the emissions. Here's how to implement it effectively.

Step 1: Create an Observable

You start by creating a new observable that will emit data when shapes are detected in the chart:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

Creating the Observable: The Observable constructor is used to create an observable that will listen for data.

Inside the Observable:

We iterate through the shapes returned from the chart using getAllShapes().

For each shape, we check if it's a horizontal line using a conditional check.

If it is, we use getShapeById to get its points and emit the price of each point using observer.next().

Completing the Observable: It is crucial to call observer.complete() after all emissions are done. This ensures the observable is considered complete, and the repeat() operator can then be utilized to invoke the function again.

Step 2: Ensure Repeating Functionality

By integrating delay(500) and repeat() operators, your observable will now emit results every 500 milliseconds. Please note that the repeat() operator will only work when the observable has completed.

Final Thoughts

Working with RXJS and observables can be highly effective for managing array data outputs over time. By ensuring that your observable completes, you'll be able to employ the repeat() function to obtain ongoing real-time data.

Now you have the foundational understanding and the code you need to run a repeating function every 500ms in RXJS. With this approach, you can efficiently filter and process your data streams as required. Happy coding!