javascript - 如何将 performance.now() 输出转换为 UTC 字符串？

Question

在我们的代码中，我们之前像这样计算事件之间的差异:

var beginTime = new Date();
// Do stuff
var endTime = new Date();
var duration = endTime.getTime() - beginTime.getTime();

console.log("Job began at " + beginTime.toUTCString()
            + " and took " + duration + " milliseconds.");

这会产生一个人类可读的字符串:

Job began at Thu Sep 28 2017 11:17:33 GMT-0500 (Central Daylight Time) and took 7000 milliseconds.

我们决定切换到 High Resolution Time通过使用更可靠的 performance.now()。但是，我们仍然希望能够包含一个人类可读的 UTC 时间字符串。

最初，我们试过这个:

var beginTime = performance.now();
// Do stuff
var endTime = performance.now();
var duration = endTime - beginTime;

console.log("Job began at " + new Date(beginTime).toUTCString() 
            + " and took " + duration + " seconds.");

我们发现持续时间是准确的，但是 new Date(performance.now()) 导致 UTC 值不准确(在撰写本文时，它提供了将近 50 年的日期过去)。

Job began at Wed Dec 31 1969 20:10:46 GMT-0600 (Central Standard Time) and took 7000 milliseconds.

是否有更好的方法将 performance.now() 的输出转换为准确的 UTC 字符串？它不必与 new Date().toUTCString() 的格式完全相同，但它应该是人类可读的。

Answer 1

我会这样做:

// mark the start time
performance.mark("start");

// ... 
//  later...
// ...
// mark the end time
performance.mark("end");

// create a measure called 'm' based on the two marks above
performance.measure("m", "start", "end");

// get the start mark, calculate its real-world timestamp using the time origin
var started = performance.getEntriesByName("start")[0];
var startedDt = new Date(performance.timing.navigationStart + started.startTime);

// get the measure we created above
var duration = performance.getEntriesByName("m")[0];
console.log(`job began on ${startedDt} and took ${duration.duration/1000.0} seconds`);

performance.clearMarks();

首先，标记持续时间测量的开始和结束时间。其次，创建持续时间测量。

稍后，您将获得开始和结束标记，通过将时间原点与开始标记的时间戳相结合来计算开始日期。最后，清除标记。

获取开始标记并不是绝对必要的...您还可以根据度量 m 计算真实世界的开始时间戳，它也有一个 startTime。我使用了开始标记，但两者都有效。

换句话说，你也可以这样做:

// get the measure we created above
var duration = performance.getEntriesByName("m")[0];
var startedDt = new Date(performance.timing.navigationStart + duration.startTime);

console.log(`job began on ${startedDt} and took ${duration.duration/1000.0} seconds`);