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How do you debug React Native?
(48 answers)
Closed 5 years ago.
How do I properly debug in React Native? From what I've seen so far, the debugging messages given aren't too useful for narrowing down where to look in my code. I just get a stack trace that only mentions dependencies in node_modules
For example:
Android emulator image (sorry, don't have enough reputation to show image on this post)
In the above error, I understsand that somewhere a non-Component object got passed in, but I have no idea how to track it down; the entire stack trace only mentions files from node_modules.
I have tried using Chrome Developer Tools as well:
Chrome Developer Tools image
I have also tried React Developer Tools and it wasn't helpful either.
How do I go about getting output from debugging that is actually helpful and linked to the code that I wrote?
Unfortunately the stack trace isn't always helpful since in this case you have to go through the bridge, and there isn't any single catch-all answer to how to get the information you need.
In this case, you're right that you most likely made a mistake returning a proper JSX object in one of your components. If you remember which components you recently added to your app, which components make up the navigator route that led to the problem, etc, you can make an educated guess as to the set of possible problematic components, and narrow that set down by commenting things out. Once that set is a reasonable size, triple-check your render methods and make sure nothing weird is going on.
You can write your own debug messages to the chrome developer console to help give yourself an idea what your app is doing (e.g. rendering this component, fetching that data from shared store, etc) using if(__DEV__) console.log("Your message here"). This will check if the app is running in a debug vs release build, and only log the messages if you are running a debug build.
You can use adb logcat for android and the XCode console for iOS to see the native debug logs, although I don't think they'll help in this case.
You can draw a picture of your component tree, put a debugger statement at the beginning of every render method, and check off components one-by-one until your app stops trying to render things and you know you've hit a problematic component (React will render components recursively, going from top-to-bottom for components on the same level in the tree).
I know it's frustrating when you can't immediately tell where the problem is by glancing at the stack trace but sometimes that's life.
Related
I'm working my way through the wonderful Serverless Stack Tutorial, and I reached the chapter on using a React ErrorBoundary to view debug information. In the chapter, it describes how one should see debug information when running the application locally (as shown below in this image from the chapter).
I've made sure that I've copied the code and set it up correctly. However, I'm not seeing the debug information in my local debug instance. I only see the fallback UI:
I'm wondering if I'm using a later version of either React or other services than used in the tutorial. I've committed my code to a separate branch in case anyone would be willing to pull/fork and try it. I'd appreciate any assistance.
Update
I found my way to this Github issue describing changes in behavior between React 17 and React 18. The issue led to this CodeSandbox example. I noticed one of the examples displayed an overlay which looked similar to the one in the tutorial example. I saw this text at the bottom:
This screen is visible only in development. It will not appear if the app crashes in production.
Open your browser’s developer console to further inspect this error.
This error overlay is powered by `react-error-overlay` used in `create-react-app`.
Searching for react-error-overlay led me to this package. I can see this package is included in my code as installed per the tutorials instructions. However, it does not seem to be running to display errors during development.
LayoutAnimation is a part of React Native that automatically animates components when the view is rendered.
The official documentation is here:
https://reactnative.dev/docs/layoutanimation
However, the examples in the docs do not work. Objects in the examples that are supposed to animate just jump from the starting position to the end position.
Here is an example of one of the Snacks in the documentation that does not appear to animate:
https://snack.expo.io/91MUQd5IH
This would lead one to the conclusion that this API is just not supported or no longer functional.
Is it the case that Layout Animation just does not work? Or if it does work under some circumstances, please share a link containing a working Snack / Gist with an extremely simple but working LayoutAnimation example.
UPDATE: LayoutAnimation possibly does not support web. Does anyone have any knowledge of this or who can refer the reader to an explanation in the docs?
LayoutAnimation is currently not supported properly in react-native-web. You can see that here: https://github.com/necolas/react-native-web#modules and here https://github.com/necolas/react-native-web/issues/1613, https://github.com/necolas/react-native-web/issues/1056. It doesn't seem to be a priority for the project at the moment so I wouldn't count on it being implemented.
On iOS/Android it's a different story. If we look here: https://reactnative.dev/docs/layoutanimation/ you can actually see this working properly by pressing play and selecting iOS for example.
On Android we have support as well but it might not work/crash. If you look over the issues open for react-native, you will see a lot of them mention issues with LayoutAnimation and Android. E.g. it crashes under certain conditions on Android: https://github.com/facebook/react-native/issues/27552 and https://github.com/facebook/react-native/issues/29919.
I don't recommend using LayoutAnimation, especially on Android, as it is highly experimental and might crash on some devices without warning.
If you want to try some more interesting animations with better performance, I recommend you try using the Animated API from ReactNative or the newer react-native-reanimated which is faster, more modern but still in alpha (I'm talking about the current, v2, version).
By my test the given link in the question post works properly:
Also, I test it on my friend's iPhone and it's worked properly too. But many of React Native features don't work properly on Web export. For example animations on RNW (React Native Web) works on Android/iOS exports but not on Web exports.
For such web situations, you should decouple the web component and make a separate file then write the desired animation on it.
I have worked with React.js on and off for several years. When I make certain kinds of mistakes in the jsx code, React.js silently fails. Here's what happens:
Compilation (with webpack) appears to succeed and produces no error messages or warnings.
But when I open my index.html file, all React components are missing from the page. (The nav bar, which I have coded directly into my index.html file, is still present and is styled correctly. Below that, where my React content is supposed to be, the page is blank.)
The browser console doesn't show any error messages.
For some mistakes, when I inspect different versions of the page source using my browser, I see that the <div data-reactroot> element was present before my breaking change, but is now absent. For other mistakes, <div data-reactroot> is present, but its contents are empty or commented out.
There is no error message to help pinpoint the source of the problem, and in my experience this same behavior can be caused by many different kinds of mistakes. So my question is, how should one debug these silent failures from React?
I'm looking for a general debugging approach, analogous to these tips for debugging CSS. Good answers might include a list of mistakes to check for, useful debugging tools, or other ways to narrow down the cause of the problem.
I'm trying to debug my gatsbyjs code in visual studio code. I followed the docs and and tried slightly different approaches like https://github.com/Microsoft/vscode-recipes/tree/master/Gatsby-js.
I can start debugging and the site builds, but my none of my breakpoints in any of my files get hit, they get instead show up as unverified.
When pausing the debug process though, I (somewhat) randomly end up in the source code of any of the external modules, and there I am able to place breakpoints that do stop...
Is there maybe some setup step or something I'm missing to make it work on page components and other react components?
Thanks for any help!
Adding a
debugger;
statement in the JS react page components definitely works for me. But be reminded that in development mode (gatsby develop), some breakpoints will get hit on startup, while others are only hit on page request. This of course depends on where you place your breakpoints.
Recently I've been setting up a development stack for React using Webpack (new for me) and of course wanted to benefit from all of the shiny conveniences that it provides (which are by the way great!). Among tons of resources I dug on the internet, the particularly good one I found was the React Webpack Cookbook, with which every step went like clockwork. However I stumbled across a hitch that has been taking me several hours to try to solve, not being able to find a solution in the aforementioned page, nor any other source: the expose-loader wouldn't expose React to global scope in Chrome (not tested on other browsers) therefore not allowing React DevTools extension to run. I tried mixing all the steps from the Cookbook, using different versions of React, minified/unprocessed, nothing worked.
The problem was trivial when discovered, but the source of the problem tricky to find: all the time I was using the localhost:8080/webpack-dev-server/ version of my development page, as suggested by the Cookbook, because it allowed me not to bother with the inability to inject <script src="http://localhost:8080/webpack-dev-server.js"></script> into html-webpack-plugin index file generator and provided sort of a nice status bar. It works perfectly since I switched to localhost:8080. Unfortunatelly I wasn't able to make it work with the localhost:8080/webpack-dev-server/ version, though I think it has something to do with the fact that under this url the page is loaded into a frame.