From 6e5a56f240d8eb9a713cea598a20e0dbf0c47c57 Mon Sep 17 00:00:00 2001
From: Rafael Fernandez Serra <rafael.serra@mhr.co.uk>
Date: Tue, 17 Dec 2019 17:14:38 +0000
Subject: [PATCH] feat(stateService): add transition option 'supercede' so
 transition can be ignored if one is pending

---
 src/state/stateService.ts           |  4 ++++
 src/transition/interface.ts         | 12 ++++++++++++
 src/transition/transitionService.ts |  1 +
 test/stateServiceSpec.ts            | 19 +++++++++++++++++++
 4 files changed, 36 insertions(+)

diff --git a/src/state/stateService.ts b/src/state/stateService.ts
index f29623e2..493dc0a6 100644
--- a/src/state/stateService.ts
+++ b/src/state/stateService.ts
@@ -338,6 +338,10 @@ export class StateService {
 
     if (!ref.valid()) return <TransitionPromise>silentRejection(ref.error());
 
+    if (options.supercede === false && getCurrent()) {
+      return <TransitionPromise>Rejection.ignored('Another transition is in progress and supercede has been set to false in TransitionOptions for the transition. So the transition was ignored in favour of the existing one in progress.').toPromise();
+    }
+
     /**
      * Special handling for Ignored, Aborted, and Redirected transitions
      *
diff --git a/src/transition/interface.ts b/src/transition/interface.ts
index 44dbc097..22e575c8 100644
--- a/src/transition/interface.ts
+++ b/src/transition/interface.ts
@@ -73,6 +73,18 @@ export interface TransitionOptions {
    * You can define your own Transition Options inside this property and use them, e.g., from a Transition Hook
    */
   custom?: any;
+  /**
+   * This option may be used to cancel the active transition (if one is active) in favour of the this one.
+   * This is the default behaviour or ui-router.
+   *
+   *
+   * - When `true`, the active transition will be canceled and new transition will begin.
+   * - when `false`, the transition will be canceled if a transition is already running. This can be useful in cases where
+   * you only want to navigate to a different state if you are not already navigating somewhere.
+   *
+   * @default `true`
+   */
+  supercede?: boolean;
   /** @internalapi */
   reloadState?: StateObject;
   /** @internalapi
diff --git a/src/transition/transitionService.ts b/src/transition/transitionService.ts
index 561e3066..8ad2af46 100644
--- a/src/transition/transitionService.ts
+++ b/src/transition/transitionService.ts
@@ -49,6 +49,7 @@ export let defaultTransOpts: TransitionOptions = {
   inherit: false,
   notify: true,
   reload: false,
+  supercede: true,
   custom: {},
   current: () => null,
   source: 'unknown',
diff --git a/test/stateServiceSpec.ts b/test/stateServiceSpec.ts
index 38f23f12..a194ad76 100644
--- a/test/stateServiceSpec.ts
+++ b/test/stateServiceSpec.ts
@@ -637,6 +637,25 @@ describe('stateService', function() {
       done();
     });
 
+    describe('when supercede TransitionOption is false', () => {
+      it('ignores transition if another transition is running', async done => {
+        $state.defaultErrorHandler(() => null);
+        await initStateTo(A);
+
+        const activeTransition = $state.transitionTo(B, {});
+        const superseded = await $state.transitionTo(C, {}, { supercede: false }).catch(err => err);
+
+        const result: Rejection = await superseded;
+        expect(result.type).toEqual(RejectType.IGNORED);
+
+        await activeTransition;
+
+        expect($state.current).toBe(B);
+
+        done();
+      });
+    });
+
     it('aborts pending transitions (last call wins)', async done => {
       $state.defaultErrorHandler(() => null);
       await initStateTo(A);