Question: Passing a struct into call.

[4ydx]

Wondering how one can pass a struct into Call and have it produce a dictionary with lowercase keys rather than uppercase exported keys.

package main

import (
  "github.com/gopherjs/gopherjs/js"
  "github.com/gopherjs/jquery"
)

var jQ = jquery.NewJQuery

type A struct {
  C string
}

func main() {
  jQ().Ready(func() {
    a := A{C: "test"}
    js.Global.Call("alert", a)
  })
}

When evaluating in the console this gives:

a
Object { $val: Object, C: "test" }
$externalize(a, A)
Object { C: "test" }

I want Object { c: "test" }. No doubt I am missing something obvious.

[myitcv]

@4ydx

I don't think there is currently a way of doing this without using a struct with a special *js.Object field in position zero; see the gotchas wiki for more details.

Consider (playground link):

package main

import (
    "github.com/gopherjs/gopherjs/js"
)

type S1 struct {
    C1 string `js:"c1"` // tag has no effect
}

type S2 struct {
    *js.Object

    C1 string `js:"c1"`  // tag has effect because of *js.Object at position 0
    C2 string
}

func main() {
    s1 := S1{C1: "S1 C1"}

    // output will be: Object {C1: "S1 C1"}
    js.Global.Get("console").Call("log", "s1", s1)

    // s2 must be a *S2; see the gotchas wiki
    s2 := &S2{Object: js.Global.Get("Object").New()} 

    // this js-tagged field must be set separate from the initialization
    // of s2; again, see the gotchas wiki
    s2.C1 = "S2 C1"

    s2.C2 = "S2 C2"

    // output will be: Object {c1: "S2 C1"}
    js.Global.Get("console").Call("log", "s2", s2)
}

But in converting your type to have a *js.Object field in position zero, beware of the gotcha that starts "In structs with *js.Object fields, the object exists in two parts..."

I'm looking to try and improve the gotchas wiki to explain this better, but I also think the use of js: tags could be made more general as you're alluding to here.

[4ydx]

Thanks very much. That clarifies things.