Add prevState to onLeave hooks (#3616)

* Add prevState to leave hook args.

* Update docs. Fill in some missed tests.

Author: timdorr

docs/API.md

@@ -350,7 +350,7 @@ Called on routes when the location changes, but the route itself neither enters
 
 If `callback` is listed as a 4th argument, this hook will run asynchronously, and the transition will block until `callback` is called.
 
-##### `onLeave()`
+##### `onLeave(prevState)`
 Called when a route is about to be exited.
 
 

docs/Glossary.md

@@ -66,10 +66,10 @@ A *hash* is a string that represents the hash portion of the URL. It is synonymo
 ## LeaveHook
 
 ```js
-type LeaveHook = () => any;
+type LeaveHook = (prevState: RouterState) => any;
 ```
 
-A *leave hook* is a user-defined function that is called when a route is about to be unmounted.
+A *leave hook* is a user-defined function that is called when a route is about to be unmounted. It receives the previous [router state](#routerstate) as its first argument. 
 
 ## Location
 

modules/TransitionUtils.js

@@ -104,8 +104,8 @@ export function runChangeHooks(routes, state, nextState, callback) {
 /**
  * Runs all onLeave hooks in the given array of routes in order.
  */
-export function runLeaveHooks(routes) {
+export function runLeaveHooks(routes, prevState) {
   for (let i = 0, len = routes.length; i < len; ++i)
     if (routes[i].onLeave)
-      routes[i].onLeave.call(routes[i])
+      routes[i].onLeave.call(routes[i], prevState)
 }

modules/__tests__/transitionHooks-test.js

@@ -90,8 +90,9 @@ describe('When a router enters a branch', function () {
         expect(nextState.routes).toContain(NewsFeedRoute)
         expect(replace).toBeA('function')
       },
-      onLeave() {
+      onLeave(prevState) {
         expect(this).toBe(NewsFeedRoute)
+        expect(prevState.routes).toContain(NewsFeedRoute)
       }
     }
 
@@ -103,8 +104,9 @@ describe('When a router enters a branch', function () {
         expect(nextState.routes).toContain(InboxRoute)
         expect(replace).toBeA('function')
       },
-      onLeave() {
+      onLeave(prevState) {
         expect(this).toBe(InboxRoute)
+        expect(prevState.routes).toContain(InboxRoute)
       }
     }
 
@@ -117,8 +119,9 @@ describe('When a router enters a branch', function () {
 
         replace('/inbox')
       },
-      onLeave() {
+      onLeave(prevState) {
         expect(this).toBe(RedirectToInboxRoute)
+        expect(prevState.routes).toContain(RedirectToInboxRoute)
       }
     }
 
@@ -135,8 +138,9 @@ describe('When a router enters a branch', function () {
         expect(nextState.routes).toContain(MessageRoute)
         expect(replace).toBeA('function')
       },
-      onLeave() {
+      onLeave(prevState) {
         expect(this).toBe(MessageRoute)
+        expect(prevState.routes).toContain(MessageRoute)
       }
     }
 
@@ -170,8 +174,9 @@ describe('When a router enters a branch', function () {
         expect(nextState.routes).toContain(DashboardRoute)
         expect(replace).toBeA('function')
       },
-      onLeave() {
+      onLeave(prevState) {
         expect(this).toBe(DashboardRoute)
+        expect(prevState.routes).toContain(DashboardRoute)
       },
       childRoutes: [ NewsFeedRoute, InboxRoute, RedirectToInboxRoute, MessageRoute, UserRoute ]
     }

modules/createTransitionManager.js

@@ -69,7 +69,7 @@ export default function createTransitionManager(history, routes) {
   function finishMatch(nextState, callback) {
     const { leaveRoutes, changeRoutes, enterRoutes } = computeChangedRoutes(state, nextState)
 
-    runLeaveHooks(leaveRoutes)
+    runLeaveHooks(leaveRoutes, state)
 
     // Tear down confirmation hooks for left routes
     leaveRoutes