[Golang] Add Method to Existing Type in External Package
When I write frontend code in Go (compiled to JavaScript via GopherJS), I want to make my code look like JavaScript code as much as possible. For example, I want to getElementById in Go as follows:
element := Document.GetElementById("elmId")
So I write a Go/GopherJS library [1] to realize my idea:
import (
"github.com/gopherjs/gopherjs/js"
)
var Document = js.Global.Get("document")
func (o *js.Object) GetElementById(id string) *js.Object {
return o.Call("getElementById", id)
}
When I compile the code, I get the following error message:
panic: interface conversion: ast.Expr is *ast.SelectorExpr, not *ast.Ident [recovered]
panic: interface conversion: ast.Expr is *ast.SelectorExpr, not *ast.Ident
After some googling [2] [3] [4], I found that it is impossible to add method to existing type in external package. But good news is that I can still do something similar as follows:
type Object struct {
*js.Object
}
var Document = &Object{js.Global.Get("document")}
func (o *Object) GetElementById(id string) *Object {
return &Object{o.Call("getElementById", id)}
}
Here we wrap *js.Object in a new defined type Object in our package [1]. And we can getElementById in Go as follows:
import (
. "github.com/siongui/godom"
)
element := Document.GetElementById("elmId")
Tested on:
- Ubuntu Linux 16.10
- Go 1.7.5
References:
| [1] | (1, 2) GitHub - siongui/godom: Make DOM manipultation in Go as similar to JavaScript as possible. (via GopherJS) |
| [2] |
| [3] |
| [4] | How to add new methods to an existing type in go? - Stack Overflow |
| [5] | dom - GopherJS bindings for the JavaScript DOM APIs (GitHub) |