Re-use getVisitAction utility function (#799)

The logic for reading an `Action` from a list of `Element` instances'
`[data-turbo-action]` attribute is still scattered across several
modules, in spite of the `getVisitAction` declared in the `util` module.

This commit replaces duplicate implementations of the `getVisitAction`
method with the utility function.

With those calls added, the `isAction` type checking utility is only
ever invoked by `getVisitAction`, so this commit moves its
implementation to the `util` module, and removes all other invocations.

src/core/drive/navigator.ts

@@ -1,9 +1,9 @@
-import { Action, isAction } from "../types"
+import { Action } from "../types"
+import { getVisitAction } from "../../util"
 import { FetchMethod } from "../../http/fetch_request"
 import { FetchResponse } from "../../http/fetch_response"
 import { FormSubmission } from "./form_submission"
 import { expandURL, getAnchor, getRequestURL, Locatable, locationIsVisitable } from "../url"
-import { getAttribute } from "../../util"
 import { Visit, VisitDelegate, VisitOptions } from "./visit"
 import { PageSnapshot } from "./page_snapshot"
 
@@ -164,9 +164,7 @@ export class Navigator {
     return this.history.restorationIdentifier
   }
 
-  getActionForFormSubmission(formSubmission: FormSubmission): Action {
-    const { formElement, submitter } = formSubmission
-    const action = getAttribute("data-turbo-action", submitter, formElement)
-    return isAction(action) ? action : "advance"
+  getActionForFormSubmission({ submitter, formElement }: FormSubmission): Action {
+    return getVisitAction(submitter, formElement) || "advance"
   }
 }

src/core/frames/frame_controller.ts

@@ -27,7 +27,7 @@ import { LinkInterceptor, LinkInterceptorDelegate } from "./link_interceptor"
 import { FormLinkClickObserver, FormLinkClickObserverDelegate } from "../../observers/form_link_click_observer"
 import { FrameRenderer } from "./frame_renderer"
 import { session } from "../index"
-import { isAction, Action } from "../types"
+import { Action } from "../types"
 import { VisitOptions } from "../drive/visit"
 import { TurboBeforeFrameRenderEvent } from "../session"
 import { StreamMessage } from "../streams/stream_message"
@@ -381,7 +381,7 @@ export class FrameController
   proposeVisitIfNavigatedWithAction(frame: FrameElement, element: Element, submitter?: HTMLElement) {
     this.action = getVisitAction(submitter, element, frame)
 
-    if (isAction(this.action)) {
+    if (this.action) {
       const { visitCachedSnapshot } = frame.delegate
 
       frame.delegate.fetchResponseLoaded = (fetchResponse: FetchResponse) => {

src/core/session.ts

@@ -13,8 +13,8 @@ import { ScrollObserver } from "../observers/scroll_observer"
 import { StreamMessage } from "./streams/stream_message"
 import { StreamMessageRenderer } from "./streams/stream_message_renderer"
 import { StreamObserver } from "../observers/stream_observer"
-import { Action, Position, StreamSource, isAction } from "./types"
-import { clearBusyState, dispatch, markAsBusy } from "../util"
+import { Action, Position, StreamSource } from "./types"
+import { clearBusyState, dispatch, getVisitAction, markAsBusy } from "../util"
 import { PageView, PageViewDelegate, PageViewRenderOptions } from "./drive/page_view"
 import { Visit, VisitOptions } from "./drive/visit"
 import { PageSnapshot } from "./drive/page_snapshot"
@@ -427,8 +427,7 @@ export class Session
   // Private
 
   getActionForLink(link: Element): Action {
-    const action = link.getAttribute("data-turbo-action")
-    return isAction(action) ? action : "advance"
+    return getVisitAction(link) || "advance"
   }
 
   get snapshot() {

src/core/types.ts

@@ -1,9 +1,5 @@
 export type Action = "advance" | "replace" | "restore"
 
-export function isAction(action: any): action is Action {
-  return action == "advance" || action == "replace" || action == "restore"
-}
-
 export type Position = { x: number; y: number }
 
 export type StreamSource = {

src/observers/form_link_click_observer.ts

@@ -1,4 +1,5 @@
 import { LinkClickObserver, LinkClickObserverDelegate } from "./link_click_observer"
+import { getVisitAction } from "../util"
 
 export type FormLinkClickObserverDelegate = {
   willSubmitFormLinkToLocation(link: Element, location: URL, event: MouseEvent): boolean
@@ -42,7 +43,7 @@ export class FormLinkClickObserver implements LinkClickObserverDelegate {
     const turboFrame = link.getAttribute("data-turbo-frame")
     if (turboFrame) form.setAttribute("data-turbo-frame", turboFrame)
 
-    const turboAction = link.getAttribute("data-turbo-action")
+    const turboAction = getVisitAction(link)
     if (turboAction) form.setAttribute("data-turbo-action", turboAction)
 
     const turboConfirm = link.getAttribute("data-turbo-confirm")

src/util.ts

@@ -1,4 +1,4 @@
-import { Action, isAction } from "./core/types"
+import { Action } from "./core/types"
 
 export type DispatchOptions<T extends CustomEvent> = {
   target: EventTarget
@@ -154,6 +154,10 @@ export function getHistoryMethodForAction(action: Action) {
   }
 }
 
+export function isAction(action: any): action is Action {
+  return action == "advance" || action == "replace" || action == "restore"
+}
+
 export function getVisitAction(...elements: (Element | undefined)[]): Action | null {
   const action = getAttribute("data-turbo-action", ...elements)