Скачать или смотреть Extracting Data from Promise in SocketIO with Raspberry Pi and NodeJS

Learn how to properly extract and display temperature data from a `Promise` in your Raspberry Pi project using SocketIO with NodeJS and React.
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This video is based on the question https://stackoverflow.com/q/62536730/ asked by the user 'Maicmi' ( https://stackoverflow.com/u/6671355/ ) and on the answer https://stackoverflow.com/a/62536942/ provided by the user 'ta4h1r' ( https://stackoverflow.com/u/13239150/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Extracting Data from Promise in SocketIO with Raspberry Pi and NodeJS

If you're diving into the world of IoT with Raspberry Pi, NodeJS, and React, you might encounter some challenges along the way. One common hurdle is extracting and displaying temperature data from a DS18B20 sensor using SocketIO for real-time updates. In this post, we'll explore how to handle a Promise in your SocketIO setup to effectively display temperature readings on the client-side without errors.

The Challenge

You have connected the DS18B20 temperature sensor to your Raspberry Pi, and you're using NodeJS along with SocketIO to emit real-time temperature readings to your React application. However, you're facing an issue where your server code returns a Promise { pending }, and when you try to use this in your React app, you encounter an error that states:

"Objects are not valid as a React child (found: object with keys {})".

This situation can be frustrating, but it's a common issue when working with asynchronous code.

Understanding the Problem

The root of the problem lies in how you're handling the asynchronous function that retrieves the temperature. When you call your broadcast() function, it returns a Promise. If you try to emit this Promise directly to the client-side, it results in an error because the client-side is unable to directly work with Promise objects.

Your Current Code Structure

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

In the code above, the variable temperature is capturing the Promise rather than the resolved temperature value.

The Solution

To resolve the issue, you need to ensure that you're extracting the data from the Promise before emitting it via SocketIO. This can be effectively achieved by modifying the getApiAndEmit function. Here's how you can do it:

Revised Code Sample

Modify your getApiAndEmit function to await the broadcast() call:

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

This ensures that when you emit the temperature data, you're passing the actual temperature value instead of the Promise.

Final Adjusted Code Excerpt

Here’s how your full server code should look after implementing the changes:

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

Conclusion

By ensuring you await the resolution of your Promise, you can effectively extract and emit the temperature data from your Raspberry Pi to your React application using SocketIO. This change not only fixes the error you were encountering but also enhances the responsiveness of your application.

Now, your project can display real-time temperature readings successfully without issues. Keep pushing the boundaries of your IoT projects, and happy coding!