Hi all,

pas2js trunk now supports async procedures and await functions. This can greatly simplify writing asynchronous code, like starting a download, handle the result, depending on the result download the next piece and so forth.
Formerly you needed some (anonymous) functions for that. Now you can write asynchronous code, that looks like normal, synchronous code.

https://wiki.freepascal.org/pas2js_AsyncAWait

Mattias

I have added the demos from the wiki page to the demo dir in the sources, fixed a small error in one of the demos.

Enjoy !

Michael.

On Thu, May 28, 2020 at 4:17 AM Mattias Gaertner via Pas2js <

This is great news! 🎉

I'm away from front-end development a bit, but I'm going to test this feature. Async/await is a very useful feature, I have been using it a lot to call non-blocking functions in Rust with more syntax sugar.

Thanks for releasing it!

I have a question.

Is it possible to use parameters-less at the await part? For example:

function foo: TJSBlob; *async*;
var
  r: TJSResponse;
begin
  r := *await* window.fetch(url);
  ...
  Result := *await* r.blob();
end;

Thank you!

The fetch/blob example exists and works as-is.

Michael.

Nice!

The Sleep method is missing in pa2js! This method is very useful, I think it should live at sysutils unit.

-------------------------------
function Sleep(ms: NativeInt): TJSPromise;
begin
  Result := TJSPromise.New(
    procedure(resolve,reject : TJSPromiseResolver)
    begin
      window.setTimeout(
      procedure()
      begin
        console.log('Done waiting');
        resolve(ms);
      end, ms);
    end);
end;
-------------------------------

Example usage:

function asyncResponse: TJSBlob; async;
var
   r: TJSResponse;
   j: TJSPromise;
begin
   r := await(window.fetch('https://jsonplaceholder.typicode.com/posts/1'));
   j := await(r.json());
   console.log(j);
   await(Sleep(5000));
   console.log('A');
   await(Sleep(5000));
   console.log('B');
end;

regards,
warleyalex

warleyalex wrote

Nice! The Sleep method is missing in pa2js! This method is very useful, I think it should live at sysutils unit.

A nice idea.

It can't live in sysutils, because it depends on web.pas (window object) and sysutils cannot depend on web.pas.
I added a new unit 'webutils.pas' and I put it in that.

I have some other ideas for functions to add to this unit, and if you have more ideas for utility routines for web.pas, please share them.

Michael.

Maybe choose another name?
Sleep() without await will return immediately and code ported from Delphi/FPC won't notice the problem.

Mattias

Well, they need to add the webutils unit, so they will need to be aware. But as a precaution, I changed the name to asyncsleep.

Michael.

Great !
I seem to remember that functions like that are available in Oxygen (inherited from C#) but supposedly with different names and usage conventions. It would be great if the "Desktop fpc would have this, as well to allow for "asynchronous loops" (making use of multiple CPUs) and similar stuff, and if the Pascal dialects could allow for writing compatible code for all of them. -Michael

From the top of my head: Among other stuff, Oxygen features "parallel loop" and "future" variable for such purpose. -Michael