LargestContentfulPaint

LargestContentfulPaint interface of the Largest Contentful Paint API provides details about the largest image or text paint before user input on a web page. The timing of this paint is a good heuristic for when the main page content is available during load.

特性

LargestContentfulPaint.element
The element that is the current largest contentful paint.
LargestContentfulPaint.renderTime
The time the element was rendered to the screen. May not be available if the element is a cross-origin image loaded without the Timing-Allow-Origin header.
LargestContentfulPaint.loadTime
The time the element was loaded.
LargestContentfulPaint.size
The intrinsic size of the element returned as the area (width * height).
LargestContentfulPaint.id
The id of the element. This property returns an empty string when there is no id.
LargestContentfulPaint.url
If the element is an image, the request url of the image.

方法

LargestContentfulPaint.toJSON()
Returns the above properties as JSON.

范例

The following example shows how to create a PerformanceObserver that listens for largest-contentful-paint entries and logs the LCP value to the console.

This example also demonstrates how to include buffered entries (those that ocurred before observer() was called), which is done by setting the buffered option to true .

Note that in this example data is only sent to the server when the user leaves the tab.

// Catch errors since some browsers throw when using the new `type` option.
// https://bugs.webkit.org/show_bug.cgi?id=209216
try {
  let lcp;
  const po = new PerformanceObserver((entryList) => {
    const entries = entryList.getEntries();
    const lastEntry = entries[entries.length - 1];
    // Update `lcp` to the latest value, using `renderTime` if it's available,
    // otherwise using `loadTime`. (Note: `renderTime` may not be available on
    // image elements loaded cross-origin without the `Timing-Allow-Origin` header.)
    lcp = lastEntry.renderTime || lastEntry.loadTime;
  });
  po.observe({type: 'largest-contentful-paint', buffered: true});
  // Send data to the server.
  addEventListener('visibilitychange', function fn() {
    if (lcp && document.visibilityState === 'hidden') {
      console.log('LCP:', lcp);
      removeEventListener('visibilitychange', fn, true);
    }
  }, true);
} catch (e) {
  // Do nothing if the browser doesn't support this API.
}
					

规范

规范 状态 Comment
Largest Contentful Paint
The definition of 'LargestContentfulPaint' in that specification.
编者草案 初始定义。

浏览器兼容性

更新 GitHub 上的兼容性数据
Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
LargestContentfulPaint Chrome 77 Edge 80 Firefox No IE No Opera Yes Safari No WebView Android 77 Chrome Android 77 Firefox Android No Opera Android Yes Safari iOS No Samsung Internet Android 12.0
element Chrome 77 Edge 80 Firefox No IE No Opera Yes Safari No WebView Android 77 Chrome Android 77 Firefox Android No Opera Android Yes Safari iOS No Samsung Internet Android 12.0
id Chrome 77 Edge 80 Firefox No IE No Opera Yes Safari No WebView Android 77 Chrome Android 77 Firefox Android No Opera Android Yes Safari iOS No Samsung Internet Android 12.0
loadTime Chrome 77 Edge 80 Firefox No IE No Opera Yes Safari No WebView Android 77 Chrome Android 77 Firefox Android No Opera Android Yes Safari iOS No Samsung Internet Android 12.0
renderTime Chrome 77 Edge 80 Firefox No IE No Opera Yes Safari No WebView Android 77 Chrome Android 77 Firefox Android No Opera Android Yes Safari iOS No Samsung Internet Android 12.0
size Chrome 77 Edge 80 Firefox No IE No Opera Yes Safari No WebView Android 77 Chrome Android 77 Firefox Android No Opera Android Yes Safari iOS No Samsung Internet Android 12.0
toJSON Chrome 77 Edge 80 Firefox No IE No Opera Yes Safari No WebView Android 77 Chrome Android 77 Firefox Android No Opera Android Yes Safari iOS No Samsung Internet Android 12.0
url Chrome 77 Edge 80 Firefox No IE No Opera Yes Safari No WebView Android 77 Chrome Android 77 Firefox Android No Opera Android Yes Safari iOS No Samsung Internet Android 12.0

图例

完整支持
完整支持
不支持
不支持