I’ve earlier written a post on how to create vanilla JS Web Components using the new API spec introduced by W3C for Custom Elements, Shadow DOM, HTML Imports and <template> tag.

The previous post showed how to create a very simple and not that useful web component. In this post I’ll teach you how to create multiple components and make them interact with each other and organizing your code. These are what I used when I learnt when I built an app using web components. You can also check out the next post about attributes.

What we’ll build

We’ll be building 3 components. The first component would be a List of people. The second component would display the information of person we select from first component. The parent component would orchestrate these components and allow us to independently develop the child components and plug them together.

Code Organization

We’ll be creating a components directory to contain all of our components. Each component will have its own directory that’ll contain the component’s HTML template, JS and stylesheets. Components that are just used to create other components and are not reused will be placed in that components directory. So in our case the directory structure will look like:

src/ index.html components/ PeopleController/ PeopleController.js PeopleController.html PeopleController.css PeopleList/ PeopleList.js PeopleList.html PeopleList.css PersonDetail/ PersonDetail.js PersonDetail.html PersonDetail.css

We’ll be using the following API from https://jsonplaceholder.typicode.com/ to get some placeholder user data. Here’s an example of how the data will look:

{ id : 1 , name : " Leanne Graham " , username : " Bret " , email : " Sincere@april.biz " , address : { street : " Kulas Light " , suite : " Apt. 556 " , city : " Gwenborough " , zipcode : " 92998-3874 " , geo : { lat : " -37.3159 " , lng : " 81.1496 " } }, phone : " 1-770-736-8031 x56442 " , website : " hildegard.org " }

Child components

People List component

Let’s start by building the PeopleList component. Create the PeopleList.html file with the following contents:

<template id= "people-list-template" > <style> .people-list__container { border : 1px solid black ; } .people-list__list { list-style : none } .people-list__list > li { font-size : 20px ; font-family : Helvetica ; color : #000000 ; text-decoration : none ; } </style> <div class= "people-list__container" > <ul class= "people-list__list" ></ul> </div> </template> <script src= "/components/PeopleController/PeopleList/PeopleList.js" ></script>

The ul.people-list__list will contain the list of the names we get. Now create the class PeopleList with the constructor , connectedCallback and render functions inside an IIFE.

( function () { const currentDocument = document . currentScript . ownerDocument ; // Private Methods will go here: // ... class PeopleList extends HTMLElement { constructor () { // If you define a constructor, always call super() first as it is required by the CE spec. super (); } connectedCallback () { // Create a Shadow DOM using our template const shadowRoot = this . attachShadow ({ mode : ' open ' }); const template = currentDocument . querySelector ( ' #people-list-template ' ); const instance = template . content . cloneNode ( true ); shadowRoot . appendChild ( instance ); } get list () { return this . _list ; } set list ( list ) { this . _list = list ; this . render (); } render () { // ... } } customElements . define ( ' people-list ' , PeopleList ); })();

In the render method, we need to create a list of people names using <li> . We will also create a CustomEvent for each of the elements. Whenever that element is clicked, its id will propagated with the event upwards in the DOM tree.

We’re doing this because it makes our child elements independent of the parent or other sibling elements. We’ll watch for this event in our parent component and update the sibling component accordingly from the parent. More on that later. Add the following code to your render function:

render () { let ulElement = this . shadowRoot . querySelector ( ' .people-list__list ' ); ulElement . innerHTML = '' ; this . list . forEach ( person => { let li = _createPersonListElement ( this , person ); ulElement . appendChild ( li ); }); }

Also create a function inside the IIFE but outside your class definition called _createPersonListElement(person) . This will be used to create li elements with the person information. Note: I’ve done it this way as it is a great way of using private function in your JS code.

function _createPersonListElement ( self , person ) { let li = currentDocument . createElement ( ' LI ' ); li . innerHTML = person . name ; li . className = ' people-list__name ' li . onclick = () => { let event = new CustomEvent ( " PersonClicked " , { detail : { personId : person . id }, bubbles : true }); self . dispatchEvent ( event ); } return li ; }

PersonDetail component

We’ve created the PeopleList component that’ll list the people by names. We also want to create a component that’ll show the people details when the person name is clicked in that component. So lets reuse the component we used in the previous tutorial, UserCard . I won’t go into the details of how I’m building this component but just put the code here. You can read more about it in the older post.

Template

Open the PersonDetail.html file and put the following code in it:

<template id= "person-detail-template" > <link rel= "stylesheet" href= "/components/PeopleController/PersonDetail/PersonDetail.css" > <div class= "card__user-card-container" > <h2 class= "card__name" > <span class= "card__full-name" ></span> ( <span class= "card__user-name" ></span> ) </h2> <p> Website: <a class= "card__website" ></a></p> <div class= "card__hidden-content" > <p class= "card__address" ></p> </div> <button class= "card__details-btn" > More Details </button> </div> </template> <script src= "/components/PeopleController/PersonDetail/PersonDetail.js" ></script>

Styling

We have now created a template for our card. Now, let’s style it using CSS. Create a new file called PersonDetail.css in UsedCard folder with the following content:

.card__user-card-container { text-align : center ; border-radius : 5px ; border : 1px solid grey ; font-family : Helvetica ; margin : 3px ; } .card__user-card-container :hover { box-shadow : 3px 3px 3px ; } .card__hidden-content { display : none ; } .card__details-btn { background-color : #dedede ; padding : 6px ; margin-bottom : 8px ; }

Component Scripting

Create the /components/PeopleController/PersonDetail/PersonDetail.js file and provide the PeopleDetail component its functionality using the following code:

( function () { const currentDocument = document . currentScript . ownerDocument ; class PersonDetail extends HTMLElement { constructor () { // If you define a constructor, always call super() first as it is required by the CE spec. super (); // Setup a click listener on <user-card> this . addEventListener ( ' click ' , e => { this . toggleCard (); }); } // Called when element is inserted in DOM connectedCallback () { const shadowRoot = this . attachShadow ({ mode : ' open ' }); const template = currentDocument . querySelector ( ' #person-detail-template ' ); const instance = template . content . cloneNode ( true ); shadowRoot . appendChild ( instance ); } // Creating an API function so that other components can use this to populate this component updatePersonDetails ( userData ) { this . render ( userData ); } // Function to populate the card(Can be made private) render ( userData ) { this . shadowRoot . querySelector ( ' .card__full-name ' ). innerHTML = userData . name ; this . shadowRoot . querySelector ( ' .card__user-name ' ). innerHTML = userData . username ; this . shadowRoot . querySelector ( ' .card__website ' ). innerHTML = userData . website ; this . shadowRoot . querySelector ( ' .card__address ' ). innerHTML = `<h4>Address</h4> ${ userData . address . suite } , <br /> ${ userData . address . street } ,<br /> ${ userData . address . city } ,<br /> Zipcode: ${ userData . address . zipcode } ` } toggleCard () { let elem = this . shadowRoot . querySelector ( ' .card__hidden-content ' ); let btn = this . shadowRoot . querySelector ( ' .card__details-btn ' ); btn . innerHTML = elem . style . display == ' none ' ? ' Less Details ' : ' More Details ' ; elem . style . display = elem . style . display == ' none ' ? ' block ' : ' none ' ; } } customElements . define ( ' person-detail ' , PersonDetail ); })()

We have created a function updatePersonDetails(userData) so that we can update this component using this function when a Person is clicked in out PeopleList component. We could have also done this using attributes.

Parent Component

Now that we have both our PeopleList component and PersonDetail component in place, lets create the parent component, PeopleController . Open the PeopleController.html file and create its template. Also import both the components in it using HTML imports.

Note: HTML imports have been depracated from the standard and are expected to be replaced by module imports. For the purpose of this tutorial we’ll use HTML imports only. You can read more on that at MDN Blog and use them accordingly.

<template id= "people-controller-template" > <link rel= "stylesheet" href= "/components/PeopleController/PeopleController.css" > <people-list id= "people-list" ></people-list> <person-detail id= "person-detail" ></person-detail> </template> <link rel= "import" href= "/components/PeopleController/PeopleList/PeopleList.html" > <link rel= "import" href= "/components/PeopleController/PersonDetail/PersonDetail.html" > <script src= "/components/PeopleController/PeopleController.js" ></script>

Open the PeopleController.css file and add the following code to it:

#people-list { width : 45% ; display : inline-block ; } #person-detail { width : 45% ; display : inline-block ; }

Open the PeopleController.js file and create the PeopleController class. We will call the API to get the data of users. This will take 2 components we defined earlier, populate the PeopleList component as well as provide the first user of this data as the initial data to the PeopleDetail component.

( function () { const currentDocument = document . currentScript . ownerDocument ; class PeopleController extends HTMLElement { constructor () { super (); this . peopleList = []; } connectedCallback () { const shadowRoot = this . attachShadow ({ mode : ' open ' }); const template = currentDocument . querySelector ( ' #people-controller-template ' ); const instance = template . content . cloneNode ( true ); shadowRoot . appendChild ( instance ); _fetchAndPopulateData ( this ); } } // Private functions here customElements . define ( ' people-controller ' , PeopleController ); })()

Now we also need to fetch the data from the API and populate the child element. In addition to that, we need to watch for the PersonClicked event in the parent component so that we can update the PersonDetail object accordingly. So create the following 2 private functions in the above file:

function _fetchAndPopulateData ( self ) { let peopleList = self . shadowRoot . querySelector ( ' #people-list ' ); fetch ( `https://jsonplaceholder.typicode.com/users` ) . then (( response ) => response . text ()) . then (( responseText ) => { const list = JSON . parse ( responseText ); self . peopleList = list ; peopleList . list = list ; _attachEventListener ( self ); }) . catch (( error ) => { console . error ( error ); }); } function _attachEventListener ( self ) { let personDetail = self . shadowRoot . querySelector ( ' #person-detail ' ); //Initialize with person with id 1: personDetail . updatePersonDetails ( self . peopleList [ 0 ]); // Watch for the event on the shadow DOM self . shadowRoot . addEventListener ( ' PersonClicked ' , ( e ) => { // e contains the id of person that was clicked. // We'll find him using this id in the self.people list: self . peopleList . forEach ( person => { if ( person . id == e . detail . personId ) { // Update the personDetail component to reflect the click personDetail . updatePersonDetails ( person ); } }) }) }

Using the component

Now that we have our components in place, we can use it in our projects. So for the sake of this tutorial, create a new HTML file called index.html and write the following code in it:

<html> <head> <title> Web Component Part 2 </title> </head> <body> <people-controller></people-controller> <script src= "https://cdnjs.cloudflare.com/ajax/libs/webcomponentsjs/1.0.14/webcomponents-hi.js" ></script> <link rel= "import" href= "./components/PeopleController/PeopleController.html" > </body> </html>

We need to add the webcomponents.js file, as not all browsers support Web Components. Note that we’re using the HTML import statement to import our component from the directory.

To run this code, you’ll need to create a static file server. If you don’t know how to do that, you can use a simple static server like static-server or json-server . For this tutorial, install static-server using:

$ npm install -g static-server

Now, navigate to your folder containing the index.html file using cd and run the server using:

$ static-server

Open your browser and go to localhost:9080, and you should see the component we just created.

You can check out the github repository I’ve created to go with these tutorials. Let me know what you think about this approach to use web components and any improvements I can make to either this post or the method I have described here. Also check out the next part in this series about attributes.