Closed
Description
#7940 (TypeScript 3.7 support) was closed as a dupe of #7431 (optional chaining and nullary coalescing support). However, TypeScript 3.7 had another syntax change that wasn't included in that: assertion functions. Unlike the other syntax changes, this isn't being standardized as part of regular JavaScript, which might be why there doesn't seem to be a Babel plugin for it.
I've been looking forward to using this feature. Will it be possible to support it in CRA?
Example Output
mkdir example;
cd example;
npx create-react-app . --typescript;
echo '
function assertIsString(val: any): asserts val is string {
if (typeof val !== "string") {
throw new AssertionError("Not a string!");
}
}
' > src/App.tsx;
yarn build;yarn run v1.17.3
$ react-scripts build
Creating an optimized production build...
=============
WARNING: You are currently running a version of TypeScript which is not officially supported by typescript-estree.
You may find that it works just fine, or you may not.
SUPPORTED TYPESCRIPT VERSIONS: >=3.2.1 <3.7.0
YOUR TYPESCRIPT VERSION: 3.7.2
Please only submit bug reports when using the officially supported version.
=============
Failed to compile.
./src/App.tsx
SyntaxError: /home/jeremy/example/src/App.tsx: Unexpected token, expected "{" (1:43)
> 1 | function assertIsString(val: any): asserts val is string {
| ^
2 | if (typeof val !== "string") {
3 | throw new AssertionError("Not a string!");
4 | }
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.