[Golang] Variadic Function Example - addEventListener
source link: http://siongui.github.io/2017/03/12/go-variadic-function-example-addEventListener/
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[Golang] Variadic Function Example - addEventListener
March 12, 2017
GopherJS [2] is a compiler from Go to JavaScript, which helps you write front-end Go code running in browsers.
To register event listeners, we can use the following code to call addEventListener method:
foo := js.Global.Get("document").Call("getElementById", "foo")
// register onclick event
foo.Call("addEventListener", "click", func(event *js.Object) {
// do something
}, false)
// or
foo.Call("addEventListener", "click", func(event *js.Object) {
// do something
})
You can pass two or three arguments to addEventListener method. But the above code is really ugly. We want to wrtie the code in idiomatic Go way, so I implement the addEventListener as a Go variadic function, which accepts two or more arguments.
The implementation of addEventListener in Go via GopherJS is as follows:
func (o *Object) AddEventListener(t string, listener func(Event), args ...interface{}) {
if len(args) == 1 {
o.Call("addEventListener", t, listener, args[0])
} else {
o.Call("addEventListener", t, listener)
}
}
where the type Object and Event is as follows:
type Object struct {
*js.Object
}
type Event struct {
*js.Object
}
JavaScript object is *js.Object in GopherJS, so the type Object and Event are in fact the wrapper for *js.Object.
Now we can register the event listeners in the following idiomatic Go way:
foo.AddEventListener("click", func(e Event) {
// do something
})
// or
foo.AddEventListener("click", func(e Event) {
// do something
}, false)
You can pass more than three arguments, but the additional arguments after third argument will not be used in my implementation.
Tested on: Ubuntu Linux 16.10, Go 1.8
References:
[3][Golang] GopherJS Synonyms with JavaScript
[5]variadic function looping through channels : golang
[6]The Go variadic function, comparing errors in Golang, solving triangles & more : golang
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