Key Strategies to Reduce HTML Reflow and Redraw: Front-End Performance Optimization

Front-end performance optimization: the key steps to reduce HTML reflow and redrawing, specific code examples are required

With the rapid development of web applications, users’ expectations for web pages Performance requirements are also getting higher and higher. Front-end performance optimization is a key part of achieving high-performance web pages. In front-end performance optimization, reducing HTML reflow and redrawing is an important direction.

HTML reflow (reflow) refers to the process in which the browser re-renders part or all of the web page. Whenever the DOM structure changes, page content changes, page size changes, style changes, etc., the browser needs to recalculate the geometric attributes of the elements and re-layout them. This process will cause performance losses. HTML repaint (repaint) refers to the process in which the browser redraws the page based on new calculation results.

To reduce HTML reflow and redraw, we can take the following key steps:

1. Use CSS3 animations instead of JavaScript animations: Using CSS3 animations can take full advantage of the browser's hardware acceleration and reduce The number of reflows and redraws. In contrast, animations implemented in JavaScript tend to trigger a lot of reflow and redraw operations. The following is a sample code using CSS3 animation:

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

.fade-in {
  animation: fadeIn 1s;
}

2. Batch operation of DOM elements: In JavaScript, frequent operation of DOM elements is one of the common causes of reflow and redrawing. In order to reduce the occurrence of this situation, we should try to use batch operation of DOM. For example, you can use DocumentFragment to insert elements in batches, and you can use display: none to hide an element and modify it multiple times before displaying it again. The following is a sample code for batch operation of DOM elements:

var fragment = document.createDocumentFragment();

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

document.body.appendChild(fragment);

3. Use virtual list technology: When a large amount of data needs to be displayed, using virtual list technology can significantly improve performance. Virtual lists only render some of the currently visible elements, not all of them. This can reduce the number of DOM nodes in the page, thereby reducing the number of reflows and redraws. The following is a sample code for a virtual list:

var list = document.getElementById('list');
var items = [];

for (var i = 0; i < 1000000; i++) {
  items.push('Item ' + i);
}

window.addEventListener('scroll', function() {
  var scrollTop = window.scrollY;
  var start = Math.floor(scrollTop / 30);
  var end = Math.ceil((scrollTop + window.innerHeight) / 30);

  list.innerHTML = items.slice(start, end).join('');
});

By implementing the above key steps, we can significantly reduce the number of HTML reflows and redraws, thereby improving the performance and user experience of web pages. Of course, in addition to the above sample code, there are many other optimization techniques that can be used to reduce reflow and redraw, which need to be selected and adjusted according to the specific application scenario. Through continuous practice and optimization, we can create more efficient web pages.

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