在此页

• 句法
• 范例
• 规范
• 浏览器兼容性
• 相关话题

startTime property returns the first recorded timestamp 的 performance entry .

注意： 此特征可用于 Web 工作者 .

The value returned by this property depends on the performance entry's type :

• " frame " - returns the timestamp when the frame was started.
• " mark " - returns the timestamp when the mark was created by a call to performance.mark() .
• " measure " - returns the timestamp when the measure was created by a call to performance.measure() .
• " navigation " - returns the timestamp with a value of " 0 ".
• " resource " - returns the timestamp immediately before the browser starts fetching the resource .

此特性是 只读 .

句法

entry.startTime;
				

返回值

A DOMHighResTimeStamp representing the first timestamp when the performance entry was created.

Note: if the performance entry has an entryType of " resource " (i.e. the entry is a PerformanceResourceTiming object), this property returns the PerformanceEntry.fetchStart timestamp .

范例

The following example shows the use of the startTime 特性。

function run_PerformanceEntry() {
  log("PerformanceEntry support ...");
  if (performance.mark === undefined) {
    log("... performance.mark Not supported");
    return;
  }
  // Create some performance entries via the mark() method
  performance.mark("Begin");
  do_work(50000);
  performance.mark("End");
  // Use getEntries() to iterate through the each entry
  var p = performance.getEntries();
  for (var i=0; i < p.length; i++) {
    log("Entry[" + i + "]");
    check_PerformanceEntry(p[i]);
  }
}
function check_PerformanceEntry(obj) {
  var properties = ["name", "entryType", "startTime", "duration"];
  var methods = ["toJSON"];
  for (var i=0; i < properties.length; i++) {
    // check each property
    var supported = properties[i] in obj;
    if (supported)
      log("..." + properties[i] + " = " + obj[properties[i]]);
    else
      log("..." + properties[i] + " = Not supported");
  }
  for (var i=0; i < methods.length; i++) {
    // check each method
    var supported = typeof obj[methods[i]] == "function";
    if (supported) {
      var js = obj[methods[i]]();
      log("..." + methods[i] + "() = " + JSON.stringify(js));
    } else {
      log("..." + methods[i] + " = Not supported");
    }
  }
}
				

规范

规范	状态	注释
Performance Timeline Level 2 The definition of 'startTime' in that specification.	候选推荐
性能时间线 The definition of 'startTime' in that specification.	推荐	初始定义。

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
startTime	Chrome Yes	Edge 12	Firefox Yes	IE Yes	Opera Yes	Safari 11	WebView Android Yes	Chrome Android Yes	Firefox Android 25	Opera Android Yes	Safari iOS 11	Samsung Internet Android Yes

图例

完整支持

完整支持

元数据

• 最后修改： Mar 18, 2019

相关话题

1. 性能时间线
2. PerformanceEntry
3. 特性

   1. duration
   2. entryType
   3. 名称
   4. startTime
4. 方法

   1. toJSON()
5. Related pages for Performance Timeline API

   1. 性能
   2. PerformanceObserver
   3. PerformanceObserverEntryList
   4. PerformanceResourceTiming
   5. Window.performance