var t0 = performance.Now()
doSomething() // <---- The function you're measuring time for
var t1 = performance.Now()
console.log("Call to doSomething took " + (t1 - t0) + " milliseconds.")
：需要导入performance类
console.time('someFunction')
someFunction() // Whatever is timed goes between the two "console.time"
console.timeEnd('someFunction')
： 传递给time()和timeEnd()方法的字符串必须匹配（以 使计时器按预期完成）。
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