Tips on how to minimize HTML reflow and redraw

HTML Optimization Tips: Practical Ways to Reduce Reflows and Redraws

As web applications and websites continue to increase in complexity, optimizing page performance becomes increasingly important The more important it is. Among various performance optimization methods, reducing reflow and redraw is a key task, which can greatly improve the loading speed and user experience of the page. This article will introduce some practical HTML optimization techniques and provide specific code examples.

Reflow and redraw are two key operations performed by the browser when rendering a page. Reflow means that when the size, position, or layout of a DOM element changes, the browser recalculates the geometric properties of the element and then re-renders the entire page or part of the page. Redrawing means that when the style attributes (such as color, font, etc.) of a DOM element change, the browser redraws the appearance of the element, but does not affect its size and position.

Frequent occurrences of reflow and redraw will lead to reduced page performance because the browser needs to consume a lot of resources to perform these operations. Here are a few practical methods that can be used to reduce reflow and redraw:

1. Use the cssText attribute
   When we dynamically modify the style of an element through js code, we can use the element's cssText attribute to do it once Modify multiple styles at once instead of modifying attributes one by one. The following is an example:

element.style.cssText = 'color: red; font-size: 16px; background-color: yellow;';

2. Use class to modify the style
   When we need to dynamically modify the style through js, it is best to use methods such as addClass and removeClass to modify the class of the element. Instead of directly modifying the style attribute of the element. Because modifying the style attribute of an element will cause reflow and redrawing, modifying the class will not have these effects. Here is an example:

element.classList.add('new-class');
element.classList.remove('old-class');

3. Using document fragmentation
   When we need to insert a large number of elements into the DOM, it is best to use document fragmentation to temporarily save these elements and then do it all at once Insert into the DOM. This can reduce the number of reflows and redraws and improve page loading speed. Here is an example:

var fragment = document.createDocumentFragment();
for (var i = 0; i < 1000; i++) {
  var element = document.createElement('div');
  element.textContent = 'Element ' + i;
  fragment.appendChild(element);
}
document.body.appendChild(fragment);

4. Using virtual DOM
   Virtual DOM is a way to represent the page structure as a JavaScript object in memory and compare the differences between the old and new virtual DOM To update the page technology. By using virtual DOM, we can update the DOM structure of the page in batches, thereby reducing the number of reflows and redraws. The following is an example of a virtual DOM using the React library:

function App() {
  return (
    <div>
      <h1>Hello, World!</h1>
      <p>This is a paragraph.</p>
    </div>
  );
}

ReactDOM.render(<App />, document.getElementById('root'));

Through the above methods, we can effectively reduce the number of reflows and redraws and improve the loading speed and performance of the page. In actual projects, we can choose appropriate methods for optimization according to specific needs and situations. I hope this article will be helpful to your HTML optimization work!

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