Typed event payloads

Contract

v0.1.15 keeps callbacks as ordinary Go functions and adds typed payloads for the intrinsic events named in v0.1.12. Payloads describe the browser event source without introducing string event names, controller registries, or a JavaScript expression language.

Callback props may keep the simple signatures from earlier patches:

<button onClick={save}><Text value={"Save"}></Text></button>
<input name="title" onInput={setTitle}></input>

They may also accept the typed payload for that event:

<button onClick={saveFromButton}><Text value={"Save"}></Text></button>
<form onSubmit={saveForm}>
  <input name="title" onInput={setTitle}></input>
  <button type="submit"><Text value={"Save"}></Text></button>
</form>

func saveFromButton(event gx.ClickEvent) {
	_ = event.TargetID
}

func saveForm(event gx.SubmitEvent) {
	event.PreventDefault()
	_ = event.FormID
	_ = event.SubmitterName
}

Payloads

This patch defines only small payload structs needed by current portal flows:

type ClickEvent struct {
	TargetID    string
	TargetName  string
	TargetValue string
	Dataset      map[string]string
}

type SubmitEvent struct {
	FormID         string
	SubmitterID    string
	SubmitterName  string
	SubmitterValue string
	Dataset         map[string]string
}

func (event *SubmitEvent) PreventDefault()
func (event SubmitEvent) DefaultPrevented() bool

type InputEvent struct {
	TargetID   string
	TargetName string
	Value      string
	Dataset    map[string]string
}

type ChangeEvent struct {
	TargetID   string
	TargetName string
	Value      string
	Dataset    map[string]string
}

type KeyboardEvent struct {
	TargetID string
	Key      string
	Code     string
	CtrlKey  bool
	AltKey   bool
	ShiftKey bool
	MetaKey  bool
	Repeat   bool
}

type FocusEvent struct {
	TargetID   string
	TargetName string
	Direction  FocusDirection
}

type FocusDirection string

const (
	FocusIn  FocusDirection = "in"
	FocusOut FocusDirection = "out"
)

String zero values mean the browser did not provide that field or the element does not have that attribute. A nil Dataset means there were no data-* attributes. Boolean zero values are false.

SubmitEvent.DefaultPrevented() is false until PreventDefault() is called. The runtime must call browser preventDefault before returning from the callback when the event was prevented. Simple func() submit callbacks keep the existing default-prevention behavior from v0.1.7.

The input and change callbacks may still use func(string) when only the current value is needed. Use payload signatures when the handler needs target identity or metadata.

Requirements

  • Callback signature validation must accept only the documented simple or payload signatures.
  • Payloads must be plain Go structs with stable fields.
  • Payloads must not expose raw JavaScript values.
  • Prevent-default control is explicit on payloads that support it.
  • Missing optional browser data is represented by zero values or empty maps, not by panics.

Boundary

This patch does not add FormData, file-list access, drag/drop data transfer, storage, fetch, or resource helpers. It only gives current callbacks typed Go payloads.

UI framework index

Sources