How to implement routing in polymer 3 using app-route - polymer-3.x

Question

I was stuck with implementing routing in polymer 3. I followed the basic guide provided on app-route documentation. But on loading the web page., I don't see any component getting loaded. I checked in shadow DOM and don't see any DOM getting rendered. Not sure what I`m missing. Here is the code.
static get properties() {
return {
page:{
type: String,
reflectToAttribute: true,
observer: '_pageChanged'
}
};
}
_pageChanged(currentPage, oldPage){
console.log('CURRENT - ', currentPage);
console.log('OLD - ', oldPage);
switch(currentPage){
case 'home':
import('./home-comp.js').then()
break;
case 'about':
import('./about-comp.js').then()
break;
case 'contact':
import('./contact-comp.js').then()
break;
default:
this.page = 'home';
}
}
<app-route
route="{{route}}"
pattern="/:page"
data="{{routeData}}"
tail="{{subroute}}">
</app-route>
<home-comp name="home"></home-comp>
<about-comp name="about"></about-comp>
<contact-comp name="contact"></contact-comp>
I don`t see lot of documentation on Polymer 3 available for checking on issues. After going through Polymer default sample web application, shop., I came across some proper solution. I would like to share it with community for any any one in need of help for same.

Answer 1

You need to have
app-route: for implementation of routing
Iron pages: Basically page switcher to load required component on demand
In app-route.,
/* observer: Its a simple observer (basically a watch which holds current value & old value) that triggers whenever data changed in page property. We read the observer and calls a function to grab its earlier */
static get properties() {
return {
page:{
type: String,
reflectToAttribute: true,
observer: '_pageChanged'
}
};
}
_pageChanged(currentPage, oldPage){
console.log('CURRENT - ', currentPage);
console.log('OLD - ', oldPage);
switch(currentPage){
case 'home':
import('./home-comp.js').then()
break;
case 'about':
import('./about-comp.js').then()
break;
case 'contact':
import('./contact-comp.js').then()
break;
default:
this.page = 'home';
}
}
<!-- pattern: reads the href property., hence set the page (pattern="/:page") property in static get property to read its data -->
<app-route route="{{route}}" pattern="/:page" data="{{routeData}}" tail="{{subroute}}"></app-route>
<ul>
<li>
Home
</li>
<li>
About
</li>
<li>
Contact
</li>
</ul>
But for first time loading., page property doe not hold any value and throws undefined.
Hence we can use complex observer to observe such changes
static get observers(){
return ['_routerChanged(routeData.page)'];
}
_routerChanged(page){
console.log('CHANGED PAGE - ', page);
this.page = page || 'home';
}
Changed route data does not load the components unless we have iron-pages. Its basically a component switcher/loader on demand. Wrap all component in main-app under <iron-pages>
<!-- selected: Data binding helps to get changed page value -->
<!-- attr-for-selected: It reads value of name attr defined in each component & matches with selected value and triggers page switch -->
<!-- fallback-selection: for 404., page/component not found handling -->
<iron-pages selected="[[page]]" attr-for-selected="name" selected-attribute="visible" fallback-selection="404">
<home-comp name="home"></home-comp>
<about-comp name="about"></about-comp>
<contact-comp name="contact"></contact-comp>
</iron-pages>
Here is the complete guide for routing implementation in polymer 3 using app-route. Hope this helps click here