代码显示：
const fn = (length, label, callback) => {
console.time(label);
for (let i = 0; i < length; i++) {
callback && callback(i);
}
console.timeEnd(label);
};
const length = 100000000;
fn(length, "1", () => {}) // very few intervals
fn(length, "2", () => {}) // regular
fn(length, "3", () => {}) // regular然后我删除了第三个参数callback，它们的执行时间非常接近..
const fn = (length, label, callback) => {
console.time(label);
for (let i = 0; i < length; i++) {
callback && callback(i);
}
console.timeEnd(label);
};
const length = 100000000;
fn(length, "1") // regular
fn(length, "2") // regular
fn(length, "3") // regular为什么？？？