Strategy for exposing a structure

[pgundlach]

My goal is to expose (export) a structure from Go to JavaScript, so I can fill the fields and call methods on the structure. I can achieve this by creating a function (the newdocfunc() below). Is there another way to export the structure? The dumb newdoc below does not work because it creates just one object (of course).

package main

import (
	"fmt"
	"os"

	"github.com/dop251/goja"
)

type document struct {
	Item string
}

func (d *document) Check() {
	fmt.Println(`~~> d.Item`, d.Item)
	fmt.Printf("~~> d %p\n", d)
}

func main() {
	runtime := goja.New()
	runtime.Set("newdocfunc", func() *document { return &document{} })
	runtime.Set("newdoc", &document{})
	_, err := runtime.RunString(`
// works fine:
const d1 = newdocfunc();
const d2 = newdocfunc();
d1.Item = "d1"
d2.Item = "d2"
d1.Check();  // prints d1
d2.Check();  // prints d2


// not okay, same object
const d3 = newdoc;
const d4 = newdoc;
d3.Item = "d3";
d4.Item = "d4";
d3.Check();  // both print d4
d4.Check();  // both print d4

`)
	if err != nil {
		fmt.Println(err)
		os.Exit(-1)
	}
}

[pgundlach]

I think this should be exposed like something new document(). I still need to learn a lot...

[pgundlach]

I think I got it to work (it was in the docs)

package main

import (
	"fmt"
	"os"

	"github.com/dop251/goja"
)

type document struct {
	Item string
}

func (d *document) Check() {
	fmt.Println(`~~> d.Item`, d.Item)
	fmt.Printf("~~> d %p\n", d)
}

func documentC(call goja.ConstructorCall, rt *goja.Runtime) *goja.Object {
	instance := &document{}
	instanceValue := rt.ToValue(instance).(*goja.Object)
	instanceValue.SetPrototype(call.This.Prototype())
	return instanceValue
}

func main() {
	runtime := goja.New()

	runtime.Set("Document", documentC)
	_, err := runtime.RunString(`

d1 = new Document();
d1.Item = "d1"
d1.Check()

d2 = new Document();
d2.Item = "d2"
d2.Check()
`)
	if err != nil {
		fmt.Println(err)
		os.Exit(-1)
	}
}

I assume this is the most JavaScript-like way to initialise a struct.