Errors and redirections

When failing a transition function (canActivate, canDeactivate, middleware) custom errors can be returned. Custom errors can be a string or an object and will be added to the error object and passed to start and navigate callbacks).
Custom errors
Custom errors can be a string (error code) or an object. They can be passed using the first argument of done callbacks or encapsulated in failed promises.
A string
router.canActivate('profile', (router) => (toState, fromState, done) => {
    done('my custom error');
});
​
router.navigate('profile', (err, state) => {
    /* Error:
    {
        code: 'CANNOT_ACTIVATE',
        segment: 'profile',
        error: 'my custom error'
    }
    /*
})
An object
router.canActivate('profile', (router) => (toState, fromState, done) => {
    done({
        why: 'because'
    });
});
​
router.navigate('profile', (err, state) => {
    /* Error:
    {
        code: 'CANNOT_ACTIVATE',
        segment: 'profile',
        why: 'because'
    }
    */
})
Redirecting after an error
When you fail a transition, you can pass a redirect property to specify what the router should do next. redirect must be an object containing the route name you want to redirect to (name) and optionally can contain params (params).
router.canActivate('profile', (router) => (toState, fromState, done) => {
    return isUserLoggedIn()
        .catch(() => Promise.reject({ redirect: { name: 'login' }}));
});
​
router.navigate('profile', (err, state) => {
    // err is null
    state.name === 'login';
});
Preventing navigation
Dependency injection
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