Execute Multiple Asynchronous Route Guards in Order

Question

I know angular route guards execute in the specified order when the canActivate function returns a simple boolean, however, what if the guards return type Observable<boolean> or Promise<boolean>?

Example in route:

{
    path: 'confirm',
    canActivate: [AuthGuard, SessionExpiredAuthGuard, CheckoutAuthGuard],
    component: CheckoutReviewOrderComponent
},

SessionExpiredAuthGuard and CheckoutAuthGuard both return type Observable<boolean>. I don't want the CheckoutAuthGuard to be executed before the SessionExpiredAuthGuard is finished retrieving it's data from the asynchronous http request.

Is there any way to force these asynchronous guards to execute in order?

Answer 1

Problem

First of all, angular doesn't support the feature to call the guards in tandem. So if first guard is asynchronous and is trying to make ajax calls, all the remaining guards will get fired even before completion of the ajax request in guard 1.

I faced the similar problem and this is how I solved it -

---

Solution

The idea is to create a master guard and let the master guard handle the execution of other guards.

The routing configuration in this case, will contain master guard as the only guard.

To let master guard know about the guards to be triggered for specific routes, add a data property in Route.

The data property is a key value pair that allows us to attach data with the routes.

The data can then be accessed in the guards using ActivatedRouteSnapshot parameter of canActivate method in the guard.

The solution looks complicated but it will assure proper working of guards once it is integrated in the application.

Following example explains this approach -

---

Example

1. Constants Object to map all application guards -

export const GUARDS = {
    GUARD1: "GUARD1",
    GUARD2: "GUARD2",
    GUARD3: "GUARD3",
    GUARD4: "GUARD4",
}

2. Application Guard -

import { Injectable } from "@angular/core";
import { Guard4DependencyService } from "./guard4dependency";

@Injectable()
export class Guard4 implements CanActivate {
    //A  guard with dependency
    constructor(private _Guard4DependencyService:  Guard4DependencyService) {}

    canActivate(next: ActivatedRouteSnapshot, state: RouterStateSnapshot): Promise<boolean> {
        return new Promise((resolve: Function, reject: Function) => {
            //logic of guard 4 here
            if (this._Guard4DependencyService.valid()) {
                resolve(true);
            } else {
                reject(false);
            }
        });
    }
}

3. Routing Configuration -

import { Route } from "@angular/router";
import { View1Component } from "./view1";
import { View2Component } from "./view2";
import { MasterGuard, GUARDS } from "./master-guard";
export const routes: Route[] = [
    {
        path: "view1",
        component: View1Component,
        //attach master guard here
        canActivate: [MasterGuard],
        //this is the data object which will be used by 
        //masteer guard to execute guard1 and guard 2
        data: {
            guards: [
                GUARDS.GUARD1,
                GUARDS.GUARD2
            ]
        }
    },
    {
        path: "view2",
        component: View2Component,
        //attach master guard here
        canActivate: [MasterGuard],
        //this is the data object which will be used by 
        //masteer guard to execute guard1, guard 2, guard 3 & guard 4
        data: {
            guards: [
                GUARDS.GUARD1,
                GUARDS.GUARD2,
                GUARDS.GUARD3,
                GUARDS.GUARD4
            ]
        }
    }
];

4. Master Guard -

import { Injectable } from "@angular/core";
import { CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot, Router } from "@angular/router";

//import all the guards in the application
import { Guard1 } from "./guard1";
import { Guard2 } from "./guard2";
import { Guard3 } from "./guard3";
import { Guard4 } from "./guard4";

import { Guard4DependencyService } from "./guard4dependency";

@Injectable()
export class MasterGuard implements CanActivate {

    //you may need to include dependencies of individual guards if specified in guard constructor
    constructor(private _Guard4DependencyService:  Guard4DependencyService) {}

    private route: ActivatedRouteSnapshot;
    private state: RouterStateSnapshot;

    //This method gets triggered when the route is hit
    public canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): Promise<boolean> {

        this.route = route;
        this.state = state;

        if (!route.data) {
            Promise.resolve(true);
            return;
        }

        //this.route.data.guards is an array of strings set in routing configuration

        if (!this.route.data.guards || !this.route.data.guards.length) {
            Promise.resolve(true);
            return;
        }
        return this.executeGuards();
    }

    //Execute the guards sent in the route data 
    private executeGuards(guardIndex: number = 0): Promise<boolean> {
        return this.activateGuard(this.route.data.guards[guardIndex])
            .then(() => {
                if (guardIndex < this.route.data.guards.length - 1) {
                    return this.executeGuards(guardIndex + 1);
                } else {
                    return Promise.resolve(true);
                }
            })
            .catch(() => {
                return Promise.reject(false);
            });
    }

    //Create an instance of the guard and fire canActivate method returning a promise
    private activateGuard(guardKey: string): Promise<boolean> {

        let guard: Guard1 | Guard2 | Guard3 | Guard4;

        switch (guardKey) {
            case GUARDS.GUARD1:
                guard = new Guard1();
                break;
            case GUARDS.GUARD2:
                guard = new Guard2();
                break;
            case GUARDS.GUARD3:
                guard = new Guard3();
                break;
            case GUARDS.GUARD4:
                guard = new Guard4(this._Guard4DependencyService);
                break;
            default:
                break;
        }
        return guard.canActivate(this.route, this.state);
    }
}

Challenges

One of the challenges in this approach is refactoring of existing routing model. However, it can be done in parts as the changes are non-breaking.

I hope this helps.

Answer 2

In addition to the answer planet_hunter, I dare to share a little improvement master-guard