Custom HTML elements are developed by inheriting HTMLElement and registering. 1. Define the class inherits HTMLElement, and controls element behavior using constructor and lifecycle methods such as connectedCallback; 2. Register elements through customElements.define(), and the tag name must contain short horizontal lines; 3. Use custom tags directly in HTML; 4. Add observedAttributes and attributeChangedCallback to implement attribute listening and interactive updates.
sure! Custom Elements are part of Web Components, which allows you to create your own HTML tags and give them specific behaviors and styles. This is useful if you want to reuse some component logic or build a maintainable UI library.
Let’s take a look at how to implement a custom element step by step.
1. Define a class to inherit HTMLElement
To create a custom element, the first step is to define a JavaScript class, which must be inherited from HTMLElement . You can add constructors, lifecycle methods, such as connectedCallback or disconnectedCallback to this class to control the behavior of elements in the page.
For example:
class MyButton extends HTMLElement {
constructor() {
super();
this.attachShadow({ mode: 'open' });
}
connectedCallback() {
this.shadowRoot.innerHTML = `
<style>
button {
background-color: #007bff;
color: white;
padding: 10px 20px;
border: none;
border-radius: 4px;
cursor: pointer;
}
</style>
<button>Click Me</button>
`;
}
} In this example, we create a class called MyButton that renders a button when inserted into the page.
2. Register custom elements
After writing the class, you need to register it with customElements.define() . The first parameter is the tag name you want to use, and the second parameter is your class name.
customElements.define('my-button', MyButton);
Note: Custom tag names must contain short horizontal lines - to avoid conflicts with future standard HTML tags. For example, my-button is legal, but mybutton cannot.
3. Use custom elements in HTML
Once the registration is successful, you can use it like a normal HTML tag:
<my-button></my-button>
The browser will automatically instantiate the class you defined and insert the contents into it. You can put it anywhere, even dynamically insert or use it multiple times without any problem.
4. Add properties and interactive functions (advanced)
If you want to make components more flexible, you can adjust the display content or behavior by observing changes in attributes.
For example, we can add a label attribute to the button:
class MyButton extends HTMLElement {
static get observedAttributes() {
return ['label'];
}
constructor() {
super();
this.attachShadow({ mode: 'open' });
}
attributeChangedCallback(name, oldValue, newValue) {
if (name === 'label') {
this.render(newValue);
}
}
connectedCallback() {
const label = this.getAttribute('label') || 'Click Me';
this.render(label);
}
render(label) {
this.shadowRoot.innerHTML = `
<style>
button {
background-color: #007bff;
color: white;
padding: 10px 20px;
border: none;
border-radius: 4px;
cursor: pointer;
}
</style>
<button>${label}</button>
`;
}
}Then use it like this:
<my-button label="Submit"></my-button>
This way, you can control the content displayed by the button through the properties.
Basically that's it. The core steps of custom elements are not complicated, but it is easy to ignore naming rules and how Shadow DOM is used. As long as you master the basic structure, you can start building your own component library.
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