android13/external/chromium-trace/catapult/third_party/polymer/components/app-route

<app-route>

app-route is an element that enables declarative, self-describing routing for a web app.

n.b. app-route is still in beta. We expect it will need some changes. We're counting on your feedback!

In its typical usage, a app-route element consumes an object that describes some state about the current route, via the route property. It then parses that state using the pattern property, and produces two artifacts: some data related to the route, and a tail that contains the rest of the route that did not match.

Here is a basic example, when used with app-location:

<app-location route="{{route}}"></app-location>
<app-route
    route="{{route}}"
    pattern="/:page"
    data="{{data}}"
    tail="{{tail}}">
</app-route>

In the above example, the app-location produces a route value. Then, the route.path property is matched by comparing it to the pattern property. If the pattern property matches route.path, the app-route will set or update its data property with an object whose properties correspond to the parameters in pattern. So, in the above example, if route.path was '/about', the value of data would be {"page": "about"}.

The tail property represents the remaining part of the route state after the pattern has been applied to a matching route.

Here is another example, where tail is used:

<app-location route="{{route}}"></app-location>
<app-route
    route="{{route}}"
    pattern="/:page"
    data="{{routeData}}"
    tail="{{subroute}}">
</app-route>
<app-route
    route="{{subroute}}"
    pattern="/:id"
    data="{{subrouteData}}">
</app-route>

In the above example, there are two app-route elements. The first app-route consumes a route. When the route is matched, the first app-route also produces routeData from its data, and subroute from its tail. The second app-route consumes the subroute, and when it matches, it produces an object called subrouteData from its data.

So, when route.path is '/about', the routeData object will look like this: { page: 'about' }

And subrouteData will be null. However, if route.path changes to '/article/123', the routeData object will look like this: { page: 'article' }

And the subrouteData will look like this: { id: '123' }

app-route is responsive to bi-directional changes to the data objects they produce. So, if routeData.page changed from 'article' to 'about', the app-route will update route.path. This in-turn will update the app-location, and cause the global location bar to change its value.

<app-location>

app-location is an element that provides synchronization between the browser location bar and the state of an app. When created, app-location elements will automatically watch the global location for changes. As changes occur, app-location produces and updates an object called route. This route object is suitable for passing into a app-route, and other similar elements.

An example of the public API of a route object that describes the URL https://elements.polymer-project.org/elements/app-location:

{
  prefix: '',
  path: '/elements/app-location'
}

Example Usage:

<app-location route="{{route}}"></app-location>
<app-route route="{{route}}" pattern="/:page" data="{{data}}"></app-route>

As you can see above, the app-location element produces a route and that property is then bound into the app-route element. The bindings are two- directional, so when changes to the route object occur within app-route, they automatically reflect back to the global location.

Hashes vs Paths

By default app-location routes using the pathname portion of the URL. This has broad browser support but it does require cooperation of the backend server. An app-location can be configured to use the hash part of a URL instead using the use-hash-as-path attribute, like so:

<app-location route="{{route}}" use-hash-as-path></app-location>

Integrating with other routing code

There is no standard event that is fired when window.location is modified. app-location fires a location-changed event on window when it updates the location. It also listens for that same event, and re-reads the URL when it's fired. This makes it very easy to interop with other routing code.

So for example if you want to navigate to /new_path imperatively you could call window.location.pushState or window.location.replaceState followed by firing a location-changed event on window. i.e.

window.history.pushState({}, null, '/new_path');
window.dispatchEvent(new CustomEvent('location-changed'));

<app-route-converter>

app-route-converter provides a means to convert a path and query parameters into a route object and vice versa. This produced route object is to be fed into route-consuming elements such as app-route.

n.b. This element is intended to be a primitive of the routing system and for creating bespoke routing solutions from scratch. To simply include routing in an app, please refer to app-location and app-route.

An example of a route object that describes https://elements.polymer-project.org/elements/app-route-converter?foo=bar&baz=qux and should be passed to other app-route elements:

{
  prefix: '',
  path: '/elements/app-route-converter',
  __queryParams: {
    foo: 'bar',
    baz: 'qux'
  }
}

__queryParams is private to discourage directly data-binding to it. This is so that routing elements like app-route can intermediate changes to the query params and choose whether to propagate them upstream or not. app-route for example will not propagate changes to its queryParams property if it is not currently active. A public queryParams object will also be produced in which you should perform data-binding operations.

Example Usage:

<iron-location path="{{path}}" query="{{query}}"></iron-location>
<iron-query-params
    params-string="{{query}}"
    params-object="{{queryParams}}">
</iron-query-params>
<app-route-converter
    path="{{path}}"
    query-params="{{queryParams}}"
    route="{{route}}">
</app-route-converter>
<app-route route='{{route}}' pattern='/:page' data='{{data}}'>
</app-route>

This is a simplified implementation of the app-location element. Here the iron-location produces a path and a query, the iron-query-params consumes the query and produces a queryParams object, and the app-route-converter consumes the path and the query params and converts it into a route which is in turn is consumed by the app-route.

Polymer.AppRouteConverterBehavior

Provides bidirectional mapping between path and queryParams and a app-route compatible route object.

For more information, see the docs for app-route-converter.