Learn how we can use new options introduced for the runGuardsAndResolvers setting for the Angular Router configuration to get a better control over when to run our resolvers and guards.

I'm pretty sure you know about Router guards and resolvers and what they are good for. If not, don't worry. I have a full course out on Egghead.io 😉.

The runGuardsAndResolvers options (here's the official doc) is actually quite a hidden functionality and not that much used. However, it has been there already since about Angular v4. The possibilities at that time were quite limited though, something like the following:

// packages/router/src/router.ts (Angular v4)
private shouldRunGuardsAndResolvers(
    curr: ActivatedRouteSnapshot, future: ActivatedRouteSnapshot,
    mode: RunGuardsAndResolvers): boolean {
  switch (mode) {
    case 'always':
      return true;

    case 'paramsOrQueryParamsChange':
      return !equalParamsAndUrlSegments(curr, future) ||
          !shallowEqual(curr.queryParams, future.queryParams);

    case 'paramsChange':
    default:
      return !equalParamsAndUrlSegments(curr, future);
  }
}

Basically there were three options, always, paramsOrQueryParamsChange and paramsChange. Given a route configuration, we can set a property runGuardsAndResolvers and set it accordingly to one of those two options.


RouterModule.forRoot([
  ...
  {
    path: 'home/:id',
    component: HomeComponent,
    ...
    runGuardsAndResolvers: 'paramsChange'
  }
])

By default if you don't specify any mode, the router will apply what is called paramsChange mode, meaning it will re-run the guards and resolvers whenever the path or path params change. Examples of URLs satisfying this condition and hence execute the guards & resolvers would be the following:

/home/1 => /home/2
/home/1 => /home/1;param1=38
/home/1;param1=38 => /home/1;param1=20

Examples not firing a change

/home/1 => /home/1?queryParam=hi
...

On the other side, when setting it to paramsOrQueryParamsChange the guards and resolvers fire on most changes to the URL and is just very similar to the always option (the only difference being probably URL fragment changes):

/home/1 => /home/2
/home/1 => /home/1;param1=38
/home/1;param1=38 => /home/1;param1=20
/home/1 => /home/1?queryParam=hi

Basically as the name suggests, it fires whenever the params (i.e. ;param1=..) changes or a query param (i.e. ?someQuery=..). One might not guess, but it also changes for al modifications of the path, like in the very first example when moving from /home/1 to /home/2.

Explore Angular Router's runGuardsAndResolvers

New Modes in Ang...