Performance.now()

performance.now()方法返回一个精确到毫秒的  DOMHighResTimeStamp 。

The returned value represents the time elapsed since the time origin.

Bear in mind the following points:

• In dedicated workers created from a Window context, the value in the worker will be lower than performance.now() in the window who spawned that worker. It used to be the same as t0 of the main context, but this was changed.
• In shared or service workers, the value in the worker might be higher than that of the main context because that window can be created after those workers.

语法

const t = window.performance.now();

示例

let t0 = window.performance.now();
doSomething();
let t1 = window.performance.now();
console.log("doSomething函数执行了" + (t1 - t0) + "毫秒.")

和JavaScript中其他可用的时间类函数（比如Date.now）不同的是，window.performance.now()返回的时间戳没有被限制在一毫秒的精确度内，而它使用了一个浮点数来达到微秒级别的精确度。

另外一个不同点是，window.performance.now()是以一个恒定的速率慢慢增加的，它不会受到系统时间的影响（可能被其他软件调整）。另外，performance.timing.navigationStart + performance.now() 约等于 Date.now()。

规范

浏览器兼容性

相关链接

• When milliseconds are not enough: performance.now() from HTML5 Rocks