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javascriptf#websharperamplifyjs

JavaScript function signatures in WebSharper

I am creating an ampify.js binding for the WebSharper. (https://github.com/aph5nt/websharper.amplifyjs). While testing my extension I found one issue with publish / subscribe implementation.

I declared a subscription handler:

let subscribeFn (data:obj) = JS.Alert(data :?> string)

I created a subscription:

Amplify.Amplify.Subscribe("tryPubSub", subscribeFn)

When I want to unsubscribe then I do:

Amplify.Amplify.Unsubscribe("tryPubSub", subscribeFn)

the problem is that, the subscribeFn is was translated into 2 different functions. If I debug the js code and check what's happening under amplify.js lib, then I get the following:

//this is what has been saved when I created a subscription
subscriptions[ topic ][ i ].callback
(L){return i.subscribeFn(L);}
.
//this is what was passed as a callback for the unsubscribe function
callback
(S){return i.subscribeFn(S);}

There is no difference in the logic, but the args are different and because of that I'm unable to unsubscribe.

Solution

  • WebSharper 3 can't optimize calls to module functions as a function value (which are represented in the quotation as a lambda), so it becomes a new function on every call site.

    A solution is to capture the module function as a local function value:

    let subscribeFn = fun (o: obj) -> subscribeFn o

    (WebSharper 4 beta already has this optimization.)