前端防抖（debounce）和节流（throttle）

前言

• 最近在react hooks项目开发中用到了防抖和节流，基于对防抖、节流实现原理的理解，结合业界优秀的hook@umijs/hooks进行了实现，在这里作一个简单的总结。
• 防抖和节流都是防止某一段时间内函数频繁触发，可是这两兄弟之间的原理却不同。
• 简答的说，防抖是某一段时间内只执行一次，而节流是间隔时间执行。

应用场景

防抖（debounce）

• search搜索框联想搜索，用户在不断输入值时，用防抖来节约请求资源。
• window触发浏览器resize的时候，用防抖来让其只触发一次。

节流（throttle）

• 鼠标不断点击触发，mousedown单位时间内只触发一次。
• 监听滚动事件，好比是否滑到底部自动加载更多，用throttle来判断。

防抖（debounce）

原生实现

function debounce(fun, delay) {
    return function (args) {
        let that = this
        let _args = args
        clearTimeout(fun.id)
        fun.id = setTimeout(function () {
            fun.call(that, _args)
        }, delay)
    }
}
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react hooks实现

首先，基于react useEffect实现一个useUpdateEffect，在防抖和节流hook的实现中都会用到：

import { useEffect, useRef } from 'react';

const useUpdateEffect: typeof useEffect = (effect, deps) => {
  const isMounted = useRef(false);

  useEffect(() => {
    if (!isMounted.current) {
      isMounted.current = true;
    } else {
      return effect();
    }
  }, deps);
};

export default useUpdateEffect;
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接着，基于react useCallback、useUpdateEffect实现函数防抖useDebounceFn：

• 参数：useDebounceFn接受三个参数：触发回调函数fn、依赖项deps、延迟时间wait；
• 返回值：useDebounceFn返回一个run、cancel方法来执行和取消触发回调函数fn；

import { DependencyList, useCallback, useEffect, useRef } from 'react';
import useUpdateEffect from '../useUpdateEffect';

type noop = (...args: any[]) => any;

export interface ReturnValue<T extends any[]> {
  run: (...args: T) => void;
  cancel: () => void;
}

function useDebounceFn<T extends any[]>(fn: (...args: T) => any, wait: number): ReturnValue<T>;
function useDebounceFn<T extends any[]>(
  fn: (...args: T) => any,
  deps: DependencyList,
  wait: number,
): ReturnValue<T>;
function useDebounceFn<T extends any[]>(
  fn: (...args: T) => any,
  deps: DependencyList | number,
  wait?: number,
): ReturnValue<T> {
  const _deps: DependencyList = (Array.isArray(deps) ? deps : []) as DependencyList;
  const _wait: number = typeof deps === 'number' ? deps : wait || 0;
  const timer = useRef<any>();

  const fnRef = useRef<noop>(fn);
  fnRef.current = fn;

  const cancel = useCallback(() => {
    if (timer.current) {
      clearTimeout(timer.current);
    }
  }, []);

  const run = useCallback(
    (...args: any) => {
      cancel();
      timer.current = setTimeout(() => {
        fnRef.current(...args);
      }, _wait);
    },
    [_wait, cancel],
  );

  useUpdateEffect(() => {
    run();
    return cancel;
  }, [..._deps, run]);

  useEffect(() => cancel, []);

  return {
    run,
    cancel,
  };
}

export default useDebounceFn;
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如何使用useDebounceFn这个防抖hook，举个例子：

效果：快速点击button会频繁调用 run，但只会在全部点击完成 500ms 后执行一次相关函数。

import React, { useState } from 'react';
import { Button } from 'antd';
import { useDebounceFn } from '../useDebounceFn';

export default () => {
  const [value, setValue] = useState(0);
  const { run } = useDebounceFn(() => {
    setValue(value + 1);
  }, 500);
  return (
    <div>
      <p
        style={{
          marginTop: 16,
        }}
      >
        {' '}
        Clicked count: {value}{' '}
      </p>
      <Button onClick={run}>Click fast!</Button>
    </div>
  );
};

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节流（throttle）

原生实现

function throttle(fun, delay) {
    let last, deferTimer
    return function (args) {
        let that = this
        let _args = arguments
        let now = +new Date()
        if (last && now < last + delay) {
            clearTimeout(deferTimer)
            deferTimer = setTimeout(function () {
                last = now
                fun.apply(that, _args)
            }, delay)
        }else {
            last = now
            fun.apply(that,_args)
        }
    }
}
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react hooks实现

import { DependencyList, useCallback, useEffect, useRef } from 'react';
import useUpdateEffect from '../useUpdateEffect';

type noop = (...args: any[]) => any;

export interface ReturnValue<T extends any[]> {
  run: (...args: T) => void;
  cancel: () => void;
}

function useThrottleFn<T extends any[]>(fn: (...args: T) => any, wait: number): ReturnValue<T>;
function useThrottleFn<T extends any[]>(
  fn: (...args: T) => any,
  deps: DependencyList,
  wait: number,
): ReturnValue<T>;
function useThrottleFn<T extends any[]>(
  fn: (...args: T) => any,
  deps: DependencyList | number,
  wait?: number,
): ReturnValue<T> {
  const _deps: DependencyList = (Array.isArray(deps) ? deps : []) as DependencyList;
  const _wait: number = typeof deps === 'number' ? deps : wait || 0;
  const timer = useRef<any>();

  const fnRef = useRef<noop>(fn);
  fnRef.current = fn;

  const currentArgs = useRef<any>([]);

  const cancel = useCallback(() => {
    if (timer.current) {
      clearTimeout(timer.current);
    }
    timer.current = undefined;
  }, []);

  const run = useCallback(
    (...args: any) => {
      currentArgs.current = args;
      if (!timer.current) {
        timer.current = setTimeout(() => {
          fnRef.current(...currentArgs.current);
          timer.current = undefined;
        }, _wait);
      }
    },
    [_wait, cancel],
  );

  useUpdateEffect(() => {
    run();
  }, [..._deps, run]);

  useEffect(() => cancel, []);

  return {
    run,
    cancel,
  };
}

export default useThrottleFn;
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如何使用useThrottleFn这个节流hook，举个例子：

效果：快速点击button会频繁调用 run，但只会每隔 500ms 执行一次相关函数。

import React, { useState } from 'react';
import { Button } from 'antd';
import { useThrottleFn } from '../useThrottleFn';

export default () => {
  const [value, setValue] = useState(0);
  const { run } = useThrottleFn(() => {
    setValue(value + 1);
  }, 500);
  return (
    <div>
      <p
        style={{
          marginTop: 16,
        }}
      >
        {' '}
        Clicked count: {value}{' '}
      </p>
      <Button onClick={run}>Click fast!</Button>
    </div>
  );
};
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总结

• 函数防抖就是法师发技能的时候要读条，技能读条没完再按技能就会从新读条。
• 函数节流就是fps游戏的射速，就算一直按着鼠标射击，也只会在规定射速内射出子弹。