Solutions to Common Reflow and Redraw Issues

Common reflow and redraw problems and solutions, specific code examples are required

In web development, performance optimization is an important topic. Reflow and redraw are common performance problems encountered during web page rendering. They can cause page freezes and resource waste. This article will introduce common reflow and redraw problems and provide some solutions to help developers optimize page performance.

1. The concepts of Reflow and Repaint

1. Reflow means that the browser calculates and determines the position of each element on the page based on the elements in the DOM tree. location and size. The page reflow process is time-consuming, so we need to minimize the number of reflows.
2. Repaint means that the browser draws elements on the page based on the style information provided by the elements in the DOM tree. Redrawing is less expensive than reflowing.

2. Common reflow and redraw problems and solutions

1. Modifying the DOM will cause reflow and redraw

When we modify When the DOM is structured or styled, the browser recalculates the position and size of elements and redraws the elements. For example, frequently modifying the style of elements through JavaScript will cause continuous reflow and redrawing, causing the page to freeze.

Solution: Minimize DOM operations. You can consolidate multiple modifications into one, or use CSS animations instead of JavaScript animations to reduce the number of redraws.

Sample code:

// 不推荐的方式
element.style.width = '100px';
element.style.height = '100px';
element.style.marginLeft = '10px';
element.style.marginTop = '10px';

// 推荐的方式
element.style.cssText = 'width: 100px; height: 100px; margin-left: 10px; margin-top: 10px;';

2. Forced synchronization layout will frequently cause reflow

In JavaScript, get the attributes of certain elements (such as offsetTop, offsetLeft , scrollTop, etc.) may cause forced synchronization of layout, thereby triggering reflow.

Solution: Try to avoid frequently retrieving these properties. You can reduce the number of reflows by caching or batch retrieval.

Sample code:

// 不推荐的方式
for (let i = 0; i < elements.length; i++) {
  const element = elements[i];
  const top = element.offsetTop;
  // 其它处理
}

// 推荐的方式
let tops = [];
for (let i = 0; i < elements.length; i++) {
  tops.push(elements[i].offsetTop);
}

3. Frequently changing the window size will cause reflow and redraw

When the window size changes, the browser will recalculate the page Layout, causing reflow and redraw.

Solution: To avoid frequently changing the window size, you can use the throttling function to control the execution frequency of the callback function for window size changes.

Sample code:

// 不推荐的方式
window.addEventListener('resize', handleResize);

// 推荐的方式
function throttle(fn, delay) {
  let timer = null;
  return function () {
    if (!timer) {
      timer = setTimeout(() => {
        fn.apply(this, arguments);
        timer = null;
      }, delay);
    }
  };
}

window.addEventListener('resize', throttle(handleResize, 200));

3. Conclusion

Reflow and redrawing issues are common and important performance optimization problems in web development. By reducing DOM operations, avoiding forced synchronization of layouts, and frequent window size changes, reflows and redraws can be effectively reduced and page performance and user experience improved. We hope that the solutions and sample code provided in this article can help developers better optimize page performance.

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