Resize Observer API用於監(jiān)聽DOM元素尺寸變化，提供更高效準(zhǔn)確的反饋。相比舊方法如window.resize事件或輪詢檢測(cè)，它直接觀察特定元素，適用於響應(yīng)式佈局、圖表重繪、懶加載等場(chǎng)景。基本用法包括創(chuàng)建實(shí)例並傳入回調(diào)函數(shù)，通過observe()方法指定目標(biāo)元素，支持多個(gè)元素觀察及清理操作。使用時(shí)需注意：初始化時(shí)不立即觸發(fā)、瀏覽器可能節(jié)流調(diào)用頻率、避免在回調(diào)中執(zhí)行重任務(wù)、部分舊環(huán)境需引入polyfill，並確保測(cè)試真實(shí)使用場(chǎng)景。

The Resize Observer API is a browser feature that lets you watch for changes in the size of one or more DOM elements. Unlike older methods, like polling with offsetWidth or relying on window resize events, Resize Observer gives you direct, efficient feedback whenever an element's dimensions actually change — even if those changes happen dynamically or without your code explicitly triggering them.

Why You'd Want to Use Resize Observer

There are plenty of situations where knowing an element's size matters. For example:

• Responsive components that need to adjust layout based on available space
• Charts or visualizations that should redraw when their container resizes
• Lazy-loading content only when it becomes visible or reaches a certain size

Before Resize Observer, developers often used workarounds like listening to window.resize , which isn't always accurate or performant. Resize Observer solves this by letting you observe specific elements instead of the whole window.

How to Set It Up (Basic Usage)

Using Resize Observer is straightforward. You create an instance of it and pass in a callback function that gets called whenever any observed element changes size.

Here's a simple example:

 const observer = new ResizeObserver(entries => {
  for (let entry of entries) {
    console.log('Element size changed:', entry.contentSize);
  }
});

observer.observe(document.getElementById('my-element'));

A few things to note:

• The callback receives an array of ResizeObserverEntry objects
• Each entry contains info like contentSize , borderBoxSize , etc.
• You can observe multiple elements by calling observe() multiple times

If you're done observing, call unobserve(element) or observer.disconnect() to clean up.

Common Pitfalls and Tips

Like any tool, Resize Observer has some gotchas you should know about:

• It doesn't fire immediately on creation — it waits until the element's size actually changes
• Throttling behavior — browsers usually throttle how often the callback runs, which is good for performance
• Avoid doing heavy work directly in the callback — consider debouncing or deferring expensive logic

Also, not all environments support it perfectly. While modern browsers do, if you're targeting older browsers like IE11, you'll need a polyfill.

One thing to keep in mind: if you're resizing the element from JavaScript (like changing its width), Resize Observer might not trigger unless the actual layout changes — so be sure to test real-world usage scenarios.

When to Reach for Resize Observer

You don't always need it. If you're just responding to the window resizing, window.addEventListener('resize', ...) still works fine. But if you're building reusable UI components or need to react to dynamic layout changes — especially in frameworks like React or Vue — Resize Observer is the better choice.

It's especially handy in component libraries, dashboards, or any layout system that needs to adapt automatically without full-page reloads or forced re-renders.

基本上就這些。

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