Javascript - 试图围绕自定义事件(Javascript - Trying to wrap my head around custom events)

 我遇到了性能API 。 您正在寻找的可能是Performance.now() ，它将为您提供微秒级的精确度。 
 
 
 
 Performance.now()方法返回一个以毫秒为单位的DOMHighResTimeStamp ，精确到千分之一毫秒，等于自PerformanceTiming.navigationStart属性和方法调用（源）以来的毫秒数。 
 
 
 MDN提供的示例是： 
 
var t0 = performance.now();
doSomething();
var t1 = performance.now();
console.log("Call to doSomething took " + (t1 - t0) + " milliseconds.")
 
 您可以使用多次测试特定短代码的性能的函数，您可以使用以下代码： 
 
/**
 * Finds the performance for a given function
 * function fn the function to be executed
 * int n the amount of times to repeat
 * return array [time elapsed for n iterations, average execution frequency (executions per second)]
 */
function getPerf(fn, n) {
  var t0, t1;
  t0 = performance.now();
  for (var i = 0; i < n; i++) {
    fn(i)
  }
  t1 = performance.now();
  return [t1 - t0, repeat * 1000 / (t1 - t0)];
}
 
 返回单次执行fn(i)花费的时间（以毫秒为单位），以及执行频率（每秒执行次数）。 n值越高，其精度越高，但测试所需的时间越长。 参数i可以包含在要测试的函数中，其中包含函数的当前迭代。 

I came across the performance API. What you're looking for is probably Performance.now(), which will give you microsecond percision.
 
 
 
The Performance.now() method returns a DOMHighResTimeStamp, measured in milliseconds, accurate to one thousandth of a millisecond equal to the number of milliseconds since the PerformanceTiming.navigationStart property and the call to the method (source).
 
 
The example MDN provides is:
 
var t0 = performance.now();
doSomething();
var t1 = performance.now();
console.log("Call to doSomething took " + (t1 - t0) + " milliseconds.")
 
A function you could use to test the performance of a specific short piece of code multiple times, you could use the following:
 
/**
 * Finds the performance for a given function
 * function fn the function to be executed
 * int n the amount of times to repeat
 * return array [time elapsed for n iterations, average execution frequency (executions per second)]
 */
function getPerf(fn, n) {
  var t0, t1;
  t0 = performance.now();
  for (var i = 0; i < n; i++) {
    fn(i)
  }
  t1 = performance.now();
  return [t1 - t0, repeat * 1000 / (t1 - t0)];
}
 
Which returns the amount of time a single execution of fn(i) takes in milliseconds, and the frequency of execution (executions per second). The higher the n value, the more precision this has, but the longer it takes to test. The argument i can be included in the function to be tested, which contains the current iteration of the function.