[Golang] Caveats of GopherJS Development

Fix runtime error via goroutine in Golang code compiled to JavaScript by GopherJS. I got runtime error when writing code to make XHR requests and also code to generate HTML via html/template

The following code is an XHR request to retrieve JSON data from server: [7]

func XhrGetWordInfo(word string) (w WordInfo, err error) {
    resp, err := http.Get(HttpWordJsonPath(word))
    if err != nil {
    defer resp.Body.Close()

    dec := json.NewDecoder(resp.Body)
    err = dec.Decode(&w)

XhrGetWordInfo is called by:


The following error showed up in browser console: [4]

Uncaught Error: runtime error: cannot block in JavaScript callback, fix by wrapping code in goroutine
Uncaught TypeError: r is not a function

After some trial and error, the correct way to make XHR requests is: [5]

go XhrGetWordInfo("sacca")

The code must be wrapped in goroutine to prevent blocking the execution.

Similar situation [6] happened again and the same solution was applied to fix the runtime error when generating HTML via html/template.

Tested on: Ubuntu Linux 15.10, Go 1.5.3, Chromium Version 48.0.2564.82 Ubuntu 15.10 (64-bit).


[1]GopherJS - A compiler from Go to JavaScript (GitHub, GopherJS Playground, godoc)
[2]Bindings · gopherjs/gopherjs Wiki · GitHub
[3]dom - GopherJS bindings for the JavaScript DOM APIs (GitHub)
[4]net/http not working · Issue #389 · gopherjs/gopherjs · GitHub
[5]use net/http by goroutine · siongui/pali@2445656 · GitHub
[6]fix bug: use html/template by goroutine · siongui/pali@39ffdf9 · GitHub
[7]handle input text enter event. Bug: net/http not working · siongui/pali@f8f1475 · GitHub