[TypeScript] Thrown values as unknown V4

Main idea is enforce you to do type checking in catch block, because if you want to get Error stacktrace, the throw value should be an Error type, if doesn't throw Error type, just a string type, you won't get stacktrace.

 

Before TS 4.0, thrown values were always considered to be of type any. Now, we can choose to regard it as of type unknown. If you’ve ever found it risky to assume that a message, stacktrace, or name property is on every possible thrown value you encounter in a catch clause, this feature may make help you sleep a little more soundly.

 

Difference between throw Error and throw a string:

Always typing errors as unknown

try {
  somethingRisky()
} catch (err: unknown) {
  if (err instanceof Error) {
      console.log(err.stack)
      throw err
  }
  else throw new Error(`${err}`)
}

 

There’s also a useUnknownInCatchVariables compilerOption flag that will make thrown values unknown across your entire project