I heard about Hermes, this tool for react native is supposed to make the app faster by converting the JS code into bytecode (Android).
Now my question is: Does this mean that the index.android.bundle in the APK file will contain only bytecode instead of JS code ?
That is correct. One of the features of Hermes is that it reduces TTI by moving JS compilation from runtime to app package build time.
You can verify this by inspecting the contents of your APK.
Related
Can we extract source code from an apk that built with react-native framework?. i've tried using dex2jar and apktools and cant seem to find anything related to source code
Nothing would prevent Apktool or dex2jar from working on a React Native application. What you are seeing is the majority of React Native application logic lives in compiled Javascript files and the native layer itself (libraries).
So I would put things into 4 buckets
Native Modules (Android - Java/Kotlin, iOS - ObjC/Swift)
RN Bridge (Java/C++)
JS (Virtual Machine - JavascriptCore / Hermes)
JS (Business logic)
The code written in Javascript is interpreted by either the runtime of JSC/Hermes in the VM. This is passed through an intermediate bridge layer of either Java/C++ to the low native portion of the phone. Hence giving the name of React Native.
So if you are decoding an application looking for source code - you'll stumble upon the java code of the bridge and any package that has an intermediate dependency in Java and not the true source code of the application you are probably looking for.
The business logic would more than likely be in a index.android.bundle file somewhere and that will be quite ugly visually as its minified. You'll need a JS beautifier to get anywhere with this path.
I've just created a new "vue native" project. I didn't change anything in the default blank app.
I managed to run it on my android device, but impossible to run it on my browser.
I run "npm start" => "metro bundler" opens.
Then I click on "Run in web browser" and I get the error below :
Again, I didn't change anything. I just want to start the default app generated automatically when starting a new project.
Anyone already faced this problem?
Thank you
"This is a known issue, and it seems running vue-native app in web is not possible at the moment, because AppEntry.js tries to import ../../App. The default packager configuration specifies .json as a valid file extension. For some reason, in web, Expo seems to be looking for App.json and ignores App.vue."
https://github.com/GeekyAnts/vue-native-core/issues/268
See the official statement from vue-native creators 2020 7th of July:
"On iOS and Android, Metro is the only component required in the JS build pipeline. We have a custom transformer (in vue-native-scripts) which Metro uses to convert .vue files into equivalent React Native code, which then effectively gets piped into the default Babel transformer used by Metro (for .js) files.
On web, though, Webpack needs to be used for intermediate transformations so that the code can run on web. Metro is used here too, but not for the transformation.
From my findings, the Expo Webpack config uses the babel-loader for handling .js files. So we'd probably need a custom Webpack loader for .vue files (or maybe some other mechanism which can do the job). My guess is that the transformer exported by vue-native-scripts would help in making a loader. But the loader needs to meet the Webpack loader API requirements and expose raw, pitch etc. as described here. We haven't worked out the details of the implementation yet.On iOS and Android, Metro is the only component required in the JS build pipeline. We have a custom transformer (in vue-native-scripts) which Metro uses to convert .vue files into equivalent React Native code, which then effectively gets piped into the default Babel transformer used by Metro (for .js) files.
On web, though, Webpack needs to be used for intermediate transformations so that the code can run on web. Metro is used here too, but not for the transformation.
From my findings, the Expo Webpack config uses the babel-loader for handling .js files. So we'd probably need a custom Webpack loader for .vue files (or maybe some other mechanism which can do the job). My guess is that the transformer exported by vue-native-scripts would help in making a loader. But the loader needs to meet the Webpack loader API requirements and expose raw, pitch etc. as described here. We haven't worked out the details of the implementation yet."
https://github.com/GeekyAnts/vue-native-core/issues/268#issuecomment-640222479
Good news that devices and on simulator running works with expo, and mostly vue-native was designed to run on mobile devices not on web :)
For the web you can have a similar codebase using vuejs.
I have been using react-native-obfuscating-transformer to obfuscate the JavaScript side of the react-native. However, now I am planning to use Hermes. I was wondering if obfuscation is recommended on top of Hermes as it compiles JavaScript to bytecode during build time.
Hermes doesn't compile the assets/index.android.bundle in your APK, which is what react-native-obfuscating-transformer claims to do. So they indeed do different things. Were you able to successfully obfuscate the assets/index.android.bundle in your apk with react-native-obfuscating-transformer? Most (perhaps all?) developers have found it unsuccessful.
I am learning React Native.
I can't find a proper documentation for metro bundler. So, I have few questions on it.
As the name suggest it creates a bundle.
But where is the bundle file located ?
Is this same as webpack ?
What is the use of that bundle file ?
A React Native app is a compiled app that is running some Javascript. Whenever you build and run your React Native project, a packager starts up called Metro. You’ve probably seen this output in your terminal before, letting your know the packager is running.
The packager does a few things:
Combines all your Javascript code into a single file, and translates any Javascript code that your device won’t understand (like JSX or some of the newer JS syntax).
Converts assets (e.g. PNG files) into objects that can be displayed by an Image component.
reference:
https://hackernoon.com/understanding-expo-for-react-native-7bf23054bbcd
Metro is a JavaScript bundler which takes in options, an entry file, and gives you a JavaScript file including all JavaScript files back. Every time you run a react native project, a compilation of many javascript files are done into a single file. This compilation is done by a bundler which is called Metro.
Answers to your questions:
1> Bundled file is located on the device itself on which you are building your app and is stored in different formats like in case of Android Plain bundling in which .bundle is created. Another format is of Indexed RAM bundle in which file is stored as binary file.
2> Webpack is also a similar type of module bundler which does bundling to ReactJS web platform and its modules are accessible through browser. Bundling process is while similar to metro.
3> These bundled files are indexed and stored in a particular numerical format and thus its easy at the run time to arrange JS files in order.
There are multiple functions of Metro bundler and you can read about the role of Metro in React Native here : https://medium.com/#rishabh0297/role-of-metro-bundler-in-react-native-24d178c7117e
Hope it helps.
Metro team keeps improving its documentation, now you can find some really good explanations at https://facebook.github.io/metro/docs/concepts (link updated):
Metro is a JavaScript bundler. It takes in an entry file and various
options, and gives you back a single JavaScript file that includes all
your code and its dependencies.
So yes, it is a sort of Webpack, but for React Native apps :)
But where is the bundle file located?
Once the bundler is started, you can check its contents at http://localhost:8081/index.bundle?platform=ios&dev=true&minify=false
(like webpack, it is served from memory, so it is not being written on your project's folder).
What is the use of that bundle file ?
This file is installed in the device for its code to be executed there. Remember that when you are writing code for a React Native application, your code is not "translated" to Java / Swift / whatever. The Native Modules will send events to a Javascript thread, and the JS thread will execute your bundled React Native code.
Im having a bit of an issue after upgrading to React Native 0.30. Using mocha, and babel I transpile the react native source before test run. I'm now seeing issues where modules cannot be found.
Here's an example:
Error: Cannot find module 'AssetRegistry'
The corresponding file can be found here https://github.com/facebook/react-native/blob/master/Libraries/Image/AssetSourceResolver.js#L21. It looks as if babel cannot locate the AssetRegistry file that is local in this directory.
Ok so it turns out that react-native-maps was calling an internal react-native library. react-native-mock has most of the internals mocked for react native however the internal library for the Image utility was not mocked.
I just used mockery to mock the library and all seems to work now.