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Discussion on: Why you should learn TypeScript today

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peerreynders profile image
peerreynders •

TIL: There needs to be a comma after the type parameter for an arrow function otherwise TS thinks it's JSX.

const wait =
  (milliseconds: number) =>
  <Value,>(executor: Executor<Value>) =>
    new Promise((resolve, reject) =>
      setTimeout(executor, milliseconds, resolve, reject)
    );
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The error message I was fighting:

"Argument of type T is not assignable to parameter of type T. T could be instantiated with an arbitrary type which could be unrelated to T."

CodeSandBox

Which seems to imply:

"The caller of the function specifies the type parameter, not the implementer"

If you refer back to my TypeScript version please note that I require Promise<T>.

Your version only gives me Promise<unknown>. The moment I put Promise<T> on rootAndRun() everything lights up red. The Promise<T> based on Factory<T> was the point of making rootAndRun() generic.

For Promise<unknown> we don't need generics to begin with. CodeSandbox

unknown is extremely useful under very specific circumstances but when overused it reminds me of the Java pre-Generic Object fiasco in terms of type safety.

that could be reused

How OO of you 😁

In this case reuse isn't the goal as this is only for testing support, so not being coupled via reuse (Beware of the Share) is a good thing.

Also in general I try to stick to the Rule of Three:

  • You must have looked at at least three systems to understand what is common across them (and therefore reusable)
  • It takes three times as much effort to make something reusable as to make it usable
  • You will receive payback after the third release.

In this case the goal was to "unroll" it enough to make it more understandable.