PerformanceEntry.duration

The duration property returns a timestamp that is the duration of the performance entry.

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

• "frame" - returns a timestamp indicating the difference between the startTimes of two successive frames.
• "mark" - returns "0" (a mark has no duration).
• "measure" - returns the timestamp that is the duration of the measure.
• "navigation" - returns the timestamp that is the difference between the PerformanceEntry.loadEventEnd and PerformanceEntry.startTime properties, respectively.例如： entry.entryType "navigation"，entry.duration 3611.26, entry.loadEventEnd 3611.2672285754975, entry.startTime 0；
• "resource" - 返回 resource 的responseEnd timestamp 和  startTime timestamp的时间差. 例如： entry.entryType "resource"，entry.duration 901.1400000000001, entry.responseEnd 2527.82, entry.startTime 1626.68， 2527.82 - 1626.68 == 901.1400000000001；

This property is 只读 .

entry.duration;

A DOMHighResTimeStamp representing the duration of the performance entry. If the duration concept doesn't apply for a particular performance metric, the browser may choose to return a duration of 0.

Note: if the performance entry has an entryType of "resource" (i.e. the entry is a PerformanceResourceTiming object), this property returns the difference between the PerformanceEntry.responseEnd and PerformanceEntry.startTime timestamps.

The following example shows the use of the duration property.

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");
    }
  }
}