Why is --isolatedModules error fixed by any import?
TypescriptTypescript Problem Overview
In a create-react-app typescript project, I tried to write this just to test some stuff quickly:
// experiment.test.ts
it('experiment', () => {
console.log('test');
});
But it gives me the following error, with a red squiggly beneath it
:
> All files must be modules when the '--isolatedModules' flag is provided.
However, if I change the file to the following, then everything apparently is fine (except for the unused import of course):
// experiment.test.ts
import { Component} from 'react'; // literally anything, don't even have to use it
it('test', () => {
console.log('test');
});
Why? What is happening here? What does --isolatedModules
actually mean/do?
Typescript Solutions
Solution 1 - Typescript
Typescript treats files without import/exports as legacy script files. As such files are not modules and any definitions they have get merged in the global namespace. isolatedModules
forbids such files.
Adding any import or export to a file makes it a module and the error disappears.
Also export {}
is a handy way to make a file a module without importing anything.
Solution 2 - Typescript
The correct way is to tell TypeScript what you want. If you don't want isolatedModules
create tsconfig.json
inside your test
directory and add:
{
"extends": "../tsconfig.json",
"compilerOptions": {
"isolatedModules": false
},
}
Adding "isolatedModules": true
to the config and then cheating TypeScript checker by adding empty export {}
smells bad code to me.
Solution 3 - Typescript
Still having error despite you exporting things from that "error file"?
Check if you don't export same name that you already export in another file
(conflict)After your fix try to stop and start your npm/yarn runner
(I experienced it cannot recover itself even after hard reload of the page especially when you have another error somewhere else)
Solution 4 - Typescript
Let's try to check isolated modules. When I checked Google, there is no direct context of it.
It basically means that you allow Typescript to compile modules in isolation.
But it comes from Typescript and has something to do with Typescript preferring modules over namespaces.
> Modules also have a dependency on a module loader (such as > CommonJs/Require.js) or a runtime which supports ES Modules. Modules > provide for better code reuse, stronger isolation and better tooling > support for bundling.
Using a create-react-app typescript project, you should have installed typescript and ts-jest (or the create-react-app should handle the dependencies based on wether you ejected the app or not).
Also ts-jest
has some information about it:
> By default ts-jest uses TypeScript compiler in the context of a > project (yours), with full type-checking and features. But it can also > be used to compile each file separately, what TypeScript calls an > ‘isolated module’. That’s what the isolatedModules option (which > defaults to false) does.
As soon as you use the export
command you are creating a module out of what is being exported.
If you are using ts-jest, you can add these settings without affecting your other modules, which the create-react-app will consist off.
"ts-jest": {
"isolatedModules": false
}
And checkout the ts-jest page (second source) for the pro's and con's.
Solution 5 - Typescript
That's because you haven't imported the function to be tested yet. Once you do that, the error will disappear. The accepted answer explains why.
Solution 6 - Typescript
how about just do
.eslintignore
add the file folder where u need to ignore from eslint so no errors on that --isolatedModules error fixed by any imports
and u can test your logics their
Solution 7 - Typescript
Problem solving, see article https://blog.csdn.net/qingfeng812/article/details/120510673
{
"compilerOptions": {
"target": "es5",
"lib": [
"dom",
"dom.iterable",
"esnext"
],
"allowJs": true,
"skipLibCheck": true,
"esModuleInterop": true,
"allowSyntheticDefaultImports": true,
"strict": true,
"forceConsistentCasingInFileNames": true,
"noFallthroughCasesInSwitch": true,
"module": "esnext",
"moduleResolution": "node",
"resolveJsonModule": true,
"isolatedModules": false,
"noEmit": true,
"jsx": "react-jsx"
},
"include": [
"src"
]
}