1. 实现

1.1 节流

// 具体实战--监控平台展示信息(websocket大量吞吐)
let throttle = (fn, timmer = 1000) => {
  let prevTime = new Date();
  return (...args) => {
    let nowTime = new Date();
    if (nowTime - prevTime > timmer) {
      fn.apply(this, args);
      prevTime = nowTime;
    }
  };
};

1.2 防抖

// 具体实战--用户输入
let debounce = (fn, offset = 1000) => {
  let timer = null;
  return (...args) => {
    if (timer) {
      clearTimeout(timer);
    }
    timer = setTimeout(() => {
      fn.apply(this, args);
    }, offset);
  };
};

2. 使用

let count = 1;
document.addEventListener(
  'scroll',
  throttle((event) => {
    console.log(count++, event);
  }),
  false
);

3. 理解

• 由于throttle()执行了，所以返回的是return里面的函数
• throttle里面包裹的匿名函数是实际被scroll事件调用的函数
• return外部的变量prevTime是闭包内的变量，能被return函数内使用
• this指针问题
• 由于...args拿到的是数组，所以使用了apply

4. hooks写法

4.1 节流

import { useCallback, useEffect, useRef } from 'react';

const useThrottle = (fn: Function, delay: number, dep: any[] = []) => {
  const { current } = useRef<{ fn: Function; prevTime: number }>({ fn, prevTime: Date.now() });

  useEffect(() => {
    // 若需要防抖的函数发生变动，或挂载点发生变动，重新挂载
    current.fn = fn;
  }, [current, fn]);

  return useCallback(
    (...args) => {
      let nowTime = Date.now();
      if (nowTime - current.prevTime > delay) {
        current.fn.apply(this, args);
        current.prevTime = nowTime;
      }
    },
    [current, delay, ...dep]
  );
};

export default useThrottle;

4.2 防抖

import { useCallback, useEffect, useRef } from 'react';

const useDebounce = (fn: Function, delay: number, dep: any[] = []) => {
  const { current } = useRef<{ fn: Function; timer: NodeJS.Timeout | null }>({ fn, timer: null });

  useEffect(() => {
    // 若需要防抖的函数发生变动，或挂载点发生变动，重新挂载
    current.fn = fn;
  }, [current, fn]);

  return useCallback(
    (...args) => {
      if (current.timer) {
        clearTimeout(current.timer);
      }
      current.timer = setTimeout(() => {
        current.fn.apply(this, args);
      }, delay);
    },
    [current, delay, ...dep]
  );
};

export default useDebounce;