TypeScript: add difference between promises and async computations#9
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avm99963 wants to merge 1 commit intoknocte:masterfrom
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TypeScript: add difference between promises and async computations#9avm99963 wants to merge 1 commit intoknocte:masterfrom
avm99963 wants to merge 1 commit intoknocte:masterfrom
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Feb 7, 2026
| * The equivalent of `await` in TypeScript, is simply the addition of the `!` character to the let statement in F#. | ||
| * In TypeScript, you can convert computation-heavy synchronous methods into asynchronous by using `async` keyword in function definition, in F# you simply wrap them with an `async{}` block (a computation expression). | ||
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| Moreover, there's a subtle difference: in TypeScript, a promise can either be fulfilled or rejected. However, in F#, an `Async<'T>` object will always return a value of type `'T` once it is run. To achieve something similar in F#, you can return a value of type [`Result<'T,'TFailure>`](https://learn.microsoft.com/en-us/dotnet/fsharp/language-reference/results) or use [`Async.Catch`](https://learn.microsoft.com/en-us/dotnet/fsharp/tutorials/async#asynccatch) to catch exceptions that are thrown during its execution. |
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hey @avm99963 thanks for this PR, glad to see you back over here :) I was gonna merge right away but then I double-checked how can you check if a promise has been "rejected" in TS/JS, and it's via try-catch! Which means it's kinda the same in F# actually, well, actually with F# you would start an Async job with an API call first, for example, two cases:
- If you use Async.StartAsTask then you get a
Task<T>, but if there was an a problem with the task, as soon as you try to retrieve its result, an exception would be thrown. - If you instead run it with Async.RunSynchronously, then the exception would be thrown right away as a result of the invocation of this
Async.RunSynchronouslyfunction.
So it looks like the error handling basics of both TS/JS and F#/.NET are similar; and if you don't want to deal with exceptions but instead with error "codes" or cases, then you would use Result DU in F#, and another approach in TS?
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