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@ItalyPaleAle
Last active October 7, 2020 03:37
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// Copyright (C) 2020 Alessandro Segala (ItalyPaleAle)
// License: MIT
// MyGoFunc fetches an external resource by making a HTTP request from Go
// The JavaScript method accepts one argument, which is the URL to request
func MyGoFunc() js.Func {
return js.FuncOf(func(this js.Value, args []js.Value) interface{} {
// Get the URL as argument
// args[0] is a js.Value, so we need to get a string out of it
requestUrl := args[0].String()
// Handler for the Promise
// We need to return a Promise because HTTP requests are blocking in Go
handler := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
resolve := args[0]
reject := args[1]
// Run this code asynchronously
go func() {
// Make the HTTP request
res, err := http.DefaultClient.Get(requestUrl)
if err != nil {
// Handle errors: reject the Promise if we have an error
errorConstructor := js.Global().Get("Error")
errorObject := errorConstructor.New(err.Error())
reject.Invoke(errorObject)
return
}
defer res.Body.Close()
// Read the response body
data, err := ioutil.ReadAll(res.Body)
if err != nil {
// Handle errors here too
errorConstructor := js.Global().Get("Error")
errorObject := errorConstructor.New(err.Error())
reject.Invoke(errorObject)
return
}
// "data" is a byte slice, so we need to convert it to a JS Uint8Array object
arrayConstructor := js.Global().Get("Uint8Array")
dataJS := arrayConstructor.New(len(data))
js.CopyBytesToJS(dataJS, data)
// Create a Response object and pass the data
responseConstructor := js.Global().Get("Response")
response := responseConstructor.New(dataJS)
// Resolve the Promise
resolve.Invoke(response)
}()
// The handler of a Promise doesn't return any value
return nil
})
// Create and return the Promise object
promiseConstructor := js.Global().Get("Promise")
return promiseConstructor.New(handler)
})
}
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