These days when you want to make a website you just can't avoid the words "VueJS" or "ReactJS" and for very good reasons, these libraries make developing a website much easier thanks to their component-based architecture and how they handle data/properties and update the relevant parts of your site accordingly it's like magic!! ✨.
But for times when I need a simple component or the element I want does not have dynamic data, I ask myself "Do I really need React/Vue for this? 🤔", well that is where web components come in.
Web components are features (not the elements themselves) that help you do a lot of things, one of which is to create a custom element that can be used just like input, div and the rest.
Let's start!.
Step 1: Define our component
One way to do this is by creating a class that implements the HTMLElement interface and give it a tag name by using the customElements.define function.
According to MDN.
The HTMLElement interface represents any HTML element. Some elements directly implement this interface, while others implement it via an interface that inherits it.
//component.js
class MyComponent extends HTMLElement {
constructor(){
super();
console.log("My component works!");
}
}
customElements.define("my-component", MyComponent); //Register the new element
Notice that the component name is hyphenated, this is because we are not allowed to make a component called something like coolcomponent, the name needs to resemble x-cool-component or cool-component
Now when we include component.js in our HTML file we can use the component we've just created.
<!-- index.html -->
<body>
<h1>Hello world!</h1>
<my-component></my-component>
</body>
And if we check the console we will see the message "My component works!", That means our component is working fine.
Step 2: Element lifecycle
Just like in Vue there are lifecycle callbacks namely
connectedCallback: this is called just after our element has been rendered.disconnectedCallback: this is called when our element is about to be removed.
//component.js
class MyComponent extends HTMLElement {
constructor(){
super();
console.log("My component works!");
}
connectedCallback(){
console.log("Mounted!")
}
disconnectedCallback(){
console.log("Unmounted!")
}
}
customElements.define("my-component", MyComponent);
We now add a button to index.html which removes our element so we can test all the lifecycle callbacks.
<!-- index.html -->
<body>
<h1>Hello world!</h1>
<my-component id="mycomponent"></my-component>
<button onclick="document.getElementById('mycomponent').remove()">Remove Component</button>
</body>
Now when we press the button our component is removed and we see the message "Unmounted!" in the console.
Step 3: Let's make something
Now that we have the basic knowledge on how to make a custom element let's use it!. A good example of this is a clock element.
Warning!!!!, CODE BOMB INCOMING!!!!! 💣💣💣
//component.js
class ClockElement extends HTMLElement {
constructor(){
super();
// Time update interval id
this.intervalID = 0;
}
pad(str){
if(str.length == 1){
str = "0"+str
}
return str;
}
//Check if hour is pm or am
pmOrAm(hour){
return Number(hour) < 12 ? "am" : "pm";
}
getTimeString(){
const date = new Date();
const seconds = date.getSeconds().toString()
const hours = date.getHours().toString()
const minutes = date.getMinutes().toString()
var hoursNumber = Number(hours)
var regularHOurs = hoursNumber-12<=0? hoursNumber : hoursNumber-12;
return this.pad(regularHOurs.toString())+":"+this.pad(minutes)+":"+this.pad(seconds)+" "+this.pmOrAm(hours)
}
disconnectedCallback(){
//Clear the timer interval
clearInterval(this.intervalID);
console.log("Unmounted")
}
connectedCallback(){
//Start the timer
this.intervalID = setInterval(()=>{
this.innerHTML = this.getTimeString()
},1000);
console.log("Mounted")
}
}
customElements.define("x-clock",ClockElement)
Let me explain what is going on here,
We have renamed the element to
ClockElementand registered it asx-clockThere is now an interval id used to identify and eventually clear the interval declared in
connectedCallbackThe
padmethod is used to add a 0 to numbers that are single digit, this makes the time look like00:09:16when it would look like0:9:16The
pmOrAmmethod returns the appropriate suffix for the time based on the hourThe
getTimeStringmethod looks complicated but it actually is not, we just get the current hour, minute and second and convert it into a nice string showing the time in 12-hour formatIn the
connectedCallback, we start a timer that sets the innerHTML of our element to the current time every 1000ms (1 second)In the
disconnectedCallbackwe clear the timer.
Now that we understand that code, let's add the element to our website.
<!-- index.html -->
<body>
<h1>Hello world!</h1>
<x-clock></x-clock>
</body>
Step 4: Attributes
Our clock looks good so far but it can be better, we will now make it display either 24-hour or 12-hour format based on an attribute of our choice. I personally like this syntax :
<x-clock military></x-clock>
so we will aim at using the existence of the attribute as a boolean.
getTimeString(military){
const date = new Date();
const seconds = date.getSeconds().toString()
const hours = date.getHours().toString()
const minutes = date.getMinutes().toString()
if(typeof military == "string"){
return this.pad(hours)+":"+this.pad(minutes)+":"+this.pad(seconds)
} else {
var hoursNumber = Number(hours)
var regularHOurs = hoursNumber-12<=0? hoursNumber : hoursNumber-12;
return this.pad(regularHOurs.toString())+":"+this.pad(minutes)+":"+this.pad(seconds)+" "+this.pmOrAm(hours)
}
}
disconnectedCallback(){
//Clear the timer interval
clearInterval(this.intervalID);
console.log("Unmounted")
}
connectedCallback(){
const military = this.getAttribute("military")
this.innerHTML = this.getTimeString(military)
this.intervalID = setInterval(()=>{
this.innerHTML = this.getTimeString(military)
},1000);
console.log("Mounted")
}
If you pay attention to the new code added in getTimeString you will see a very strange statement typeof military == "string", this is there because when we set the attribute like this:
<x-clock military></x-clock>
we get the value of the attribute as "" which in javascript is equivalent to false, so if(military) will return false even if the attribute exists
Now we can now choose to display either in 12-hour or 24-hour format by adding an attribute !!
<!-- index.html -->
<body>
<h1>Hello world!</h1>
<x-clock></x-clock>
<x-clock military></x-clock>
</body>
Step 5: Reactive state
Our element currently does not change state in runtime even if our attribute has, that looks like it can be improved upon. So we will now make the element reactive to attribute changes.
To do this we use a MutationObserver, this helps us watch for any changes to our element.
A good place to put this is in the element constructor. The MutationObserver constructor returns a MutationObserver that invokes a specified callback whenever there are changes to our element.
constructor(){
super();
// Time update interval id
this.intervalID = 0;
this.observer = new MutationObserver((mutations)=>{
for(var mutation of mutations){
if(mutation.type == "attribute"){
// React to changes
}
}
});
this.observer.observe(this,{
attributes: true // Only listen for attribute changes
});
}
We assign the observer to this.observer instead of const observer because we need to clean up the listener in our disconnectedCallback.
disconnectedCallback(){
//Disconnect observer
this.observer.disconnect();
//Clear the timer interval
clearInterval(this.intervalID);
console.log("Unmounted")
}
When the attribute changes we need to display the accurate time format, and for that, we also need to change const military to this.military so we can access the variable from the MutationObserver.
constructor(){
super();
// Time update interval id
this.intervalID = 0;
this.observer = new MutationObserver((mutations)=>{
for(var mutation of mutations){
if(mutation.type == "attribute"){
// React to changes
this.military = this.getAttribute("military");
}
}
});
this.observer.observe(this,{
attributes: true // Only listen for attribute changes
});
}
//Other code
connectedCallback(){
this.military = this.getAttribute("military")
this.innerHTML = this.getTimeString(this.military);
this.intervalID = setInterval(()=>{
this.innerHTML = this.getTimeString(this.military);
},1000);
console.log("Mounted");
}
We are done 🎉🎉🎉🎉🎉🎉🎉🎉
Not only have we just made our custom element but we made it react dynamically to changes. This only scratches the surface of what web components can do and I can't wait to see the great things you guys will use it for.
Once again this is not a replacement for VueJS (Or it's counterparts), it is only an alternative for when Vue is overkill
Top comments (8)
Tip: instead of using a MutationObserver, one could just use the standard available observedAttributes property together with the changedAttributeCallback function to observe changes :-)
Nice article! If I may ask, how's the browser support for this feature as of now?
Can I Use. Let's just say it's on the way ;)
Yeah, it's on the way but there is also a polyfill so you don't have to wait
Nice nice nice!
Why not add the #webcomponents tag to this post for more exposure?
Thanks that's a good idea, don't know why I did not think of that 😅.
Awesome article. Thanks for the short and crisp introduction. I love tutorials with good examples. Looking forward to your next posts.
Yeah! Truly good examples! A big thumb up.