proposal: syscall/js: AsyncFuncOf

[jcbhmr]

Proposal Details

Let you do this:

jsFunction := js.FuncOf(func(_ js.Value, args []js.Value) any {
  return args[0].Float() + args[1].Float()
})
jsAsyncFunction := js.AsyncFuncOf(func(_ js.Value, args []js.Value) any {
  time.Sleep(100 * time.Millisecond)
  return args[0].Float() + args[1].Float()
})

How you could do the same thing today without js.AsyncFuncOf():

// disclaimer: I have no idea if this code works or not
jsAsyncFunction := js.FuncOf(func(_ js.Value, args []js.Value) any {
  executor := js.FuncOf(func(_ js.Value, executorArgs []js.Value) any {
    resolve := executorArgs[0]
    reject := executorArgs[1]
    go func() {
      defer func() {
        if r := recover(); r != nil {
          reject.Invoke(r)
        }
      }()
      time.Sleep(100 * time.Millisecond)
      resolve.Invoke(args[0].Float() + args[1].Float())
    }()
    return js.Value{}
  })
  defer executor.Release()
  return js.Global().Get("Promise").New(executor)
})

...but that's quite a lot of code.

Also this would correspond very nicely with the ()=>{} & async ()=>{} counterparts. ()=>{} => js.FuncOf() and async ()=>{} => js.AsyncFuncOf(). Nice and tidy.

This idea was referenced already: #69720

[gabyhelp]

Related Issues

• proposal: syscall/js: method or function to await a js.Value #69720
• proposal: syscall/js: `ValueOf` should accept `[]js.Value` and `map[string]js.Value` as analogs of `[]any` and `map[string]any` #60335
• syscall/js: enable a JS Promise pattern for Funcs #52581

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[ianlancetaylor]

CC @golang/js

[johanbrandhorst]

Instead of adding this to syscall/js, as suggested previously, maybe this should live in an golang.org/x package? Or maybe even in some third party package. I don't know that we need this when the basic build blocks are there to get this functionality today.

[earthboundkid]

I've definitely written this myself before. I'm not sure if it should be in the standard library, but it's for sure a common need.