了解 DOM 事件

DOM Events is what makes a webpage interactive. Using DOM events is what makes a page click or a form submit, it lets developers create an engaging user experience.

Some examples of DOM Events is when a user clicks the mouse, when a webpage has loaded, when an image has loaded, when a HTML form is submitted, and when a user presses a key.

In this article we will simplify key concepts in DOM Events and explore how to handle them.

1. addEventListener

addEventListener, attaches an event handler to elements, it allows you to define how the element reacts to the users interaction to the page.

Example: The code below is adding a 'click' event to display the cocktails details when the image is clicked.

`img.addEventListener('click', () => handleClick(cocktail));`

2. querySelector

querySelector, allows you to select an element using CSS-like selectors. It’s one of the most versatile ways to target elements.

Example: This code is creating a collapsible section on the webpage. document.querySelectorAll is selecting all the h3 elements on the webpage and returns a NodeList of all the matching elements.

const setupCollapsibles = () => {
  const collapsibles = document.querySelectorAll('.collapsible h3');

3. getElementById and getElementsByClassName

getElementById targets a single element by its unique id.

Similarly, getElementsByClassName selects all elements with a specific class and returns them as a collection.

Example: Below, getElementById finds an element by its id attribute in the HTML document.

It is being used here to access the specific form inputs, new-name, new-ingredients, new-image, new-recipe and retrieves their values.

These values are then stored in the properties of the newCocktail object which is defined with const.

This way, when the user submits a form to create a new cocktail it is stored in a structured way inside the newCocktail object.

const newCocktail = {
      name: document.getElementById('new-name').value,
      ingredients: document.getElementById('new-ingredients').value.split(', '),
      image: document.getElementById('new-image').value,
      recipe: document.getElementById('new-recipe').value,
    }; 

4. DOMContentLoaded

The DOMContentLoaded event ensures your JavaScript runs only after the DOM is fully loaded, preventing errors from trying to access elements before they're available.

Example: DOMContentLoaded, is an event that fires when the initial HTML document has been completely loaded and parsed, without waiting for stylesheets, images, or other external resources to fully load.

It ensures that the DOM is fully built and accessible, so you can safely interact with elements in the HTML, such as adding event listeners or manipulating the DOM.

In the code below, the browser is telling you, that the document is now available and the user can start interacting with it.

document.addEventListener('DOMContentLoaded', () => {
  setupEditListener();
  setupDeleteListener();
});

Final Notes

DOM events are fundamental in making a webpage interactive and engaging for users. By understanding and utilizing core methods like addEventListener, querySelector, getElementById, and getElementsByClassName, you can create dynamic user interfaces that respond to clicks, form submissions, and more.

Additionally, the DOMContentLoaded event ensures that your scripts are executed only after the DOM is fully loaded, preventing potential errors and ensuring smooth user interaction.

In summary, DOM events allow you to:

• Attach event handlers with addEventListener for responsive interactivity.

• Select elements with querySelector or getElementById to dynamically update content.

• Manage event-triggered actions based on user input, such as form submissions.

• Ensure your scripts run at the right time using DOMContentLoaded.

With these techniques, you can transform static web pages into interactive experiences that enhance user engagement.

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