Best Practices for Efficient DOM Manipulation in JavaScript

This article explores best practices for efficient JavaScript DOM operations, aiming to improve performance and reduce error risk. DOM (Document Object Model) is a web page API that allows JavaScript to access and manipulate the content and structure of HTML documents.

1. Use CSS class instead of inline style

   When styleing DOM elements, it is best to use CSS classes instead of inline styles. CSS classes are easy to modify and reuse, while inline styles are difficult to manage and maintain.

   For example, instead of writing:

   document.getElementById('button').style.backgroundColor = 'red';

   This is better:

   .button-style {
       background-color: red;
   }

   Then apply the style like this:

   let cardButton = document.getElementById('button');
   cardButton.classList.add('button-style');

2. Cache Selector

   Selector cache can improve the efficiency of DOM operation code. Store the selector results in a variable for reuse and avoid repeated query of the DOM.

   For example, instead of writing:

   document.querySelector('#button').addEventListener('click', function() {
       // do something
   });
   document.querySelector('#button').className = "enabled";

   This is better:

   const myButton = document.querySelector('#button');
   myButton.addEventListener('click', function() {
       // do something
   });
   myButton.className = "enabled";

3. Using event delegation

   Event delegate refers to attaching an event listener to a parent element and then processing events that occur on its child elements. If there are many child elements, this is more efficient than attaching an event listener to each child element separately. Event delegates can also make the code more concise and easy to maintain.

   Example:

   Here, we add a click event to the parent container, instead of adding a click event to each button. In the event handler, use the getElementById, querySelector or getElementsByClassName methods to select elements based on the CSS selector.

4. Avoid usinginnerHTML

   innerHTMLAlthough it is easy to manipulate DOM and HTML elements, it has security risks and is vulnerable to cross-site scripting (XSS) attacks. Additionally, when updating HTML content dynamically, innerHTML is slower than other methods, because it requires the browser to parse and render the entire HTML content of the element.

   Alternative methods include: textContent, appendChild().

   const newText = document.createElement('p');
   const parentElement = document.getElementById('heading');
   parentElement.appendChild(newText);

5. Avoid nesting elements in selector

   In some cases, nesting elements in selectors is not best practice. This will reduce the reusability of the selector and increase the difficulty of code maintenance. If the HTML structure changes, the selector may no longer match the target element.

   For example, instead of writing:

   document.querySelector('#parent .child');

   This is better:

   const parent = document.querySelector('#parent');
   const child = parent.querySelector('.child');

   Another example:

   // 不佳实践
   let menuHead = document.querySelector('header > nav > ul.menu');
   
   // 良好实践
   let menuHead = document.querySelector('.menu');

6. Limit the number of DOM operations

   DOM operation can be slow, especially when pages are modified frequently. Minimize the number of DOM operations to optimize performance. For example, if you need to change the text of a paragraph and the background color of the button, it is best to change it at the same time rather than separately.

7. Conclusion

   Efficient DOM operations are essential to creating fast and user-experienced web applications. Following best practices, including reducing the number of DOM changes and using event delegates, can speed up code and reduce the risk of performance issues. It is also crucial to test and evaluate the code to discover and fix problems.

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