I am new in React Native. Right now, I am studying Props and State. I wanted to try the FlatList Component in this doc https://facebook.github.io/react-native/docs/flatlist. However, I am getting this error.
You're using typed JavaScript known as Type script.
If you want to use TypeScript (I highly encourage it, then you can do so by following below tutorial):
Migrating to TypeScript:
https://facebook.github.io/react-native/blog/2018/05/07/using-typescript-with-react-native
To just get rid of the error!
state = {selected : (new Map())};
TypeScript Migration Continued...
Adding TypeScript
The next step is to add TypeScript to your project. The following commands will:
add TypeScript to your project
add React Native TypeScript Transformer to your project
initialize an empty TypeScript config file, which we'll configure next
add an empty React Native TypeScript Transformer config file, which we'll - configure next
adds typings for React and React Native
Okay, let's go ahead and run these.
yarn add --dev typescript
yarn add --dev react-native-typescript-transformer
yarn tsc --init --pretty --jsx react
touch rn-cli.config.js
yarn add --dev #types/react #types/react-native
The tsconfig.json file contains all the settings for the TypeScript compiler. The defaults created by the command above are mostly fine, but open the file and uncomment the following line:
{
/* Search the config file for the following line and uncomment it. */
// "allowSyntheticDefaultImports": true, /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
}
The rn-cli.config.js contains the settings for the React Native TypeScript Transformer. Open it and add the following:
module.exports = {
getTransformModulePath() {
return require.resolve('react-native-typescript-transformer');
},
getSourceExts() {
return ['ts', 'tsx'];
},
};
Migrating to TypeScript
Rename the generated App.js and __tests_/App.js files to App.tsx. index.js needs to use the .js extension. All new files should use the .tsx extension (or .ts if the file doesn't contain any JSX).
If you tried to run the app now, you'd get an error like object prototype may only be an object or null. This is caused by a failure to import the default export from React as well as a named export on the same line. Open App.tsx and modify the import at the top of the file:
-import React, { Component } from 'react';
+import React from 'react'
+import { Component } from 'react';
Some of this has to do with differences in how Babel and TypeScript interoperate with CommonJS modules. In the future, the two will stabilize on the same behaviour.
At this point, you should be able to run the React Native app.
I'm just getting started with react native and have created a base app with create-react-native-app.
I did some restructuring and made a few new folders and renamed the App.js to Home.js. I modified the app.json to contain an entry point that references the new Home.js file. When I load the app, nothing happens. There's no error, it just stays on the expo screen.
.
-components
-screens
-Home
Home.js
-config
-node_modules
-tests
app.json
app.json file:
{
"expo": {
"sdkVersion" : "23.0.0",
"entryPoint" : "./screens/Home/Home.js"
}
}
How do you define the entry point of the app?
if you are using Expo, you have to specify the entrypoint in your app.json file like this:
{
"expo": {
"entryPoint": "./src/app/index.js"
}
}
then, inside that file you need to register the app with Expo.registerRootComponent(YOUR_MAIN_APP_COMPONENT)
import Expo from 'expo'
...
class App extends Component {
...
}
export default Expo.registerRootComponent(App);
this way you can add your entry file wherever you want.
You need to update the app.json so that the entryPoint is the new path to the App.js.
{
"expo": {
"entryPoint": "./src/App.js",
...
}
}
However using Expo.registerRootComponent(App) causes the following error in SDK 32:
undefined is not an object (evaluating '_expo.default.registerRootComponent')
It can be fixed by importing registerRootComponent explicitly, rather than trying to access it via Expo.registerRootComponent.
Here is a sample App.js.
import { registerRootComponent } from 'expo';
class App extends React.Component {
...
}
export default registerRootComponent(App);
For Expo Projects
According to the current Expo documentation, if you want a different entry point than the App.js file, you can update the package.json - add a main field with the path to the desired entry point. Then inside the entry point file you'll have to also have to register the root component of the app. Expo was doing this automatically, when the entry point wasn't specified and was the App.js file
package.json
{
"main": "my/customEntry.js"
}
entryPointFile.js
import { registerRootComponent } from 'expo';
import MyRootComponent from './MyRoot';
registerRootComponent(MyRootComponent);
What if I want to name my main app file something other than App.js? - https://docs.expo.io/versions/latest/sdk/register-root-component/#what-if-i-want-to-name-my
If your project is in managed workflow setup (the default one), as stated in the doc, you must import the registerRootComponent and call it with your root component as argument, in the file you wish to be the main one:
import { registerRootComponent } from 'expo';
const AnyName() { ... } // Your root component
registerRootComponent(AnyName)
And then, in your package.json file, change the "main" to this file relative path, like
{
"main": "src/main.js"
}
I created project by react-native-script. In default entrypoint of app (App.js), you export App which import from your entry.
- node_modules
- App.js
- build
- main.js
File App.js:
import App from './build/main'
export default App
I also prefer to put all sources in a separated folder, for instance src/, and I found a different solution:
in my package.json, generated by expo cli, I see that main attribute is node_modules/expo/AppEntry.js.
I copied node_modules/expo/AppEntry.js to src/expoAppEntry.js and just changed the App import to import App from './App'; so it points to my *src/App.tsx`
then of course I changed the package.json main attribute to src/expoAppEntry.js.
See a working example here https://github.com/fibo/tris3d-app/blob/master/src/expoAppEntry.js
For those who are using Expo with typescript, you dont have to add .tsx at the end of the entrypoint in app.json. For example your entrypoint can be:
{
"expo": {
"entryPoint": "./app/components/AppEntryPoint/App.component",
"name": "Sample App",
...
}
...
}
In this example the name of entrypoint component is App.Component.tsx. But not mentioning the extension will also work. Apart from this, in the root component, writing export default registerRootComponent(AppComponent) or registerRootComponent(AppComponent) both should work as exporting a component from a file only means that other files can use it as well. Not writing it should not be an issue here because we have mentioned in app.json that this is the root component. App.json will look up and start building the structure of the app from there itself.
The entry point can be found in node_modules/expo/AppEntry.js..
This is in Expo Typescript...
import registerRootComponent from 'expo/build/launch/registerRootComponent';
import App from '../../src/App';
registerRootComponent(App);
In this you can change your entry point. Initially it is set to App, Look the import statement where that component is coming from.
I created a fresh react native project (version 0.47.1). Now I'm trying to write a new component for my react native app.
/my-component.jsx
import React from 'react';
import {Text} from 'react-native';
export default class MyComponent extends React.Component {
render() {
return <Text>My Component</Text>
}
}
/index.android.js
import React, { Component } from 'react';
import { AppRegistry } from 'react-native';
import MyComponent from './my-component';
export default class Test extends Component {
render() {
return (
<MyComponent />
);
}
}
AppRegistry.registerComponent('test', () => Test);
The packager throws the following error:
error: bundling failed: "Unable to resolve module `./my-component` from `<project_root_dir>/index.android.js`:
could not resolve `<project_root_dir>/my-component' as a folder: it did not contain a package, nor an index file"
Adding the file extension to the import results in the same error, except with the file extension appended to the paths in the error.
The same error goes for dependencies added via npm. In any case the path shown in the error exists.
It seems like you have moved the entry file i.e index.android.js into a custom directory i.e test => (test/index.android.js). For this purpose it cannot locate the entry file. Placing the index.android.js again into the root directory will solve the problem.
If you want to change the entry point of the project you can refer the following:
https://github.com/facebook/react-native/issues/3442
Change entry file path of android and ios in react-native project
I have started learning react native. I am struggling in the simple react native project while importing new js [example Home.js] in index.android.js
I'm getting the following error"
Module does not exist in the module map or in these directories.
UnableToResolveError: Unable to resolve module .src/Components/home/Home/Home.js from C:\Users\Magi\Dictionary1\index.android.js: Module does not exist in the module map or in these directories:
import React, { Component } from 'react';
import {
AppRegistry,
StyleSheet,
Text,
View
} from 'react-native';
import Home from '.src/Components/home/Home/Home.js';
Some unwanted import can be causing the issue.
For me, this state was creating the issue.
import { exec } from "child_process";
If Home.js and index.android.js are in the same directory, you can replace
import Home from '.src/Components/home/Home/Home.js';
with
import Home from './Home.js';
But if your src folder is at the same level as index.android.js, src needs to be preceded by ./ instead of .:
import Home from './src/Components/home/Home/Home.js';
I'm new to react native so this must be easy:
My (simple) application:
index.android.js
import SearchContainer from './components/SearchContainer.jsx';
AppRegistry.registerComponent('MyFirstApp', () => SearchContainer);
and in components/SearchContainer.jsx:
import React, { Component } from 'react';
export default class SearchContainer extends Component {
....
}
but I'm getting
Requiring unknown module "./components/SearchContainer.jsx".If you are sure the module is there, try restarting the packager or running "npm install".
I've tried a moving the SearchContainer to the same directory as index.android.js and I get the same thing.
Thanks a bunch in advance, friends!
Ok, I found out a way this will work, but I'm not sure what the science behind it is - I guess "jsx" is a take over from React that simply doesn't belong.
I simply changed "jsx" to "js" and it worked.