1. export function throttle(callback, timeout) {
    2.   let startTime = 0;
    4.   return (...args) => {
    5.     let nowTime = Date.now();
    6.     // 第一次会执行，后面 startTime = nowTime
    7.     if(nowTime - startTime >= timeout) {
    8.       callback.call(this, ...args);
    9.       startTime = nowTime;
    10.     }
    11.   }
    12. }