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HTML Settings

Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

              <div class="message">
  Alert! This is an alert message!

<div class="messages">  
    message-text="Hey, how are you?"
    message-text="I'm good, thanks for asking."
              body .message {
  width: 50%;
  background-color: #ff3333;
  padding: 20px;

/* Below is just for nice presentation of the example! */

:root {
  --profile-photo-size: 32px;

body {
  font-family: sans-serif;

.messages {
  width: 400px;
              // This template could also be stored in HTML as a `<template>`
const TEMPLATE = `
<div class="message">
  <img class="profile-photo">
  <div class="author"></div>
  <div class="message-text"></div>
.message {
  float: left;
  position: relative;
  box-sizing: border-box;
  width: 300px;
  border-radius: 5px;
  box-shadow: 0 0 5px rgba(0, 0, 0, 0.2);
  background-color: #fafafa;
  padding: 10px 10px 10px calc(var(--profile-photo-size) + 20px);
  margin: 5px 0;

.message.self {
  float: right;
  background-color: #eff7ff;

.message time {
  font-size: 75%;
  opacity: 0.5;

.profile-photo {
  position: absolute;
  left: 10px;
  top: 10px;
  width: var(--profile-photo-size);
  height: var(--profile-photo-size);

.author {
  font-weight: 700;

// The class extends `HTMLElement`, but actually it could extend any element, such as `HTMLImageElement`
class CustomMessage extends HTMLElement {
  constructor() {
    this.innerHTML = TEMPLATE;
  // Whenever an attibute is changed, this function is called. A switch statement is a good way to handle the various attributes.
  // Note that this also gets called the first time the attribute is set, so we do not need any special initialisation code.
  attributeChangedCallback(name, oldValue, newValue) {
    switch(name) {
      case 'author':
        this.querySelector('.author').innerText = newValue;
        this.querySelector('.message').classList.toggle('self', newValue === 'Me');
      case 'profile-photo':
        this.querySelector('.profile-photo').setAttribute('src', newValue);
      case 'message-text':
        this.querySelector('.message-text').innerText = newValue;
      case 'time':
        this.querySelector('time').innerText = newValue;
  // We need to specify which attributes will be watched for changes. If an attribute is not included here, attributeChangedCallback will never be called for it
  static get observedAttributes() {
    return ['author', 'profile-photo', 'message-text', 'time'];

// Now that our class is defined, we can register it
customElements.define('custom-message', CustomMessage);
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