Typescript annotation error for default React Native app?

Question

When creating a fresh React Native project and opening the default app.js file in VSCode, this line;

const App: () => React$Node = () => {

returns

Type annotations can only be used in TypeScript files.

as a VSCode problem.

Am I suppose to have typescript installed with React Native, or is this some kind of other issue with VSCode or something? Surely React Native isn't releasing their default app.js file with an error.

Here's the contents of the problem.

{
    "resource": "/d:/App/sw_lbi_app/App.js",
    "owner": "typescript",
    "code": "8010",
    "severity": 8,
    "message": "Type annotations can only be used in TypeScript files.",
    "source": "ts",
    "startLineNumber": 27,
    "startColumn": 12,
    "endLineNumber": 27,
    "endColumn": 28
}

themefield · Accepted Answer · 2020-05-31 01:11:03Z

7

const App: () => React$Node = () => {

Type annotations can only be used in TypeScript files.

In case you want to leave this line of Facebook's code to stay peacefully in Microsoft's VS Code, there is a Setting switch to turn off the TypeScript-style validation in a .js file.

Open Preferences => Settings, search javascript.validate, and locate

Uncheck it, and re-open App.js file. The validation will be gone.

PS: There is an option to make this setting change in User scope or Workspace scope.

answered May 31, 2020 at 1:11

themefield

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Comments

emeraldsanto · Accepted Answer · 2020-05-02 19:23:37Z

3

That's Flow, not TypeScript. Simply remove the types and your code will run without problem.

answered May 2, 2020 at 19:23

emeraldsanto

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8 Comments

srb633 Over a year ago

Okay done, does react native expect the user's default app.js to support flow?

emeraldsanto Over a year ago

Yes as Flow is a tool built by Facebook, which is also behind React Native.

srb633 Over a year ago

Okay i'll look into installing it haha. Thank you

emeraldsanto Over a year ago

You'll be much better off learning TypeScript, Flow is practically dead nowadays. You don't need to learn any of them if you prefer to stick to JavaScript

srb633 Over a year ago

First time I've heard of both. What use does a language like typescript or flow have to react native apps?

|

MasterPiece · Accepted Answer · 2020-09-24 17:22:39Z

1

It is Flow not TypeScript as mentioned Yanick.

VSC doesn't support it by default, so if you want to keep it the way it is, you can just install Flow Language Support extension in your IDE.

answered Sep 24, 2020 at 17:22

MasterPiece

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