vueuse filter 解析

createFilterWrapper

js 复制代码

/**
 * @internal
 */
export function createFilterWrapper<T extends AnyFn>(filter: EventFilter, fn: T) {
  function wrapper(this: any, ...args: ArgumentsType<T>) {
    return new Promise<Awaited<ReturnType<T>>>((resolve, reject) => {
      // make sure it's a promise
      Promise.resolve(filter(() => fn.apply(this, args), { fn, thisArg: this, args }))
        .then(resolve)
        .catch(reject);
    });
  }
  return wrapper;
}

createFilterWrapper 返回的函数wrapper就是被eventFilter处理过的函数，比如传入的fn希望被节流，当filter是throttleFilter，那么wrapper就是一个节流的函数。

// 创建一个节流函数（只创建一次）

js 复制代码

const throttledFn = useThrottleFn(() => {
  console.log('throttled function');
});

// 多次调用这个节流函数（每次调用会创建一个新Promise，但执行会受到节流控制）

js 复制代码

throttledFn();
throttledFn();
throttledFn();

也就是当执行 throttledFn()就会执行 filter(() => fn.apply(this, args), { fn, thisArg: this, args })

本质上这个filter 才是最终的「节流了的函数」，即 throttledFn <==> filter

和lodash一样节流/防抖，如何用createFilterWrapper实现呢？

如const fn = _.debounce(fn, 200, { maxWait: 1000 }) ，使用createFilterWrapper 如下：

js 复制代码

fn = createFilterWrapper(
    debounceFilter(200, { maxWait: 1000 }),
    fn,
  );

throttleFilter

js 复制代码

// throttleFilter函数内返回的filter

const filter: EventFilter = (_invoke) => {
    const duration = toValue(ms);
    const elapsed = Date.now() - lastExec;
    const invoke = () => lastValue = _invoke();

    clear();

    if (duration <= 0) {
      lastExec = Date.now();
      return invoke();
    }

    if (elapsed > duration && (leading || !isLeading)) {
      lastExec = Date.now();
      invoke();
    } else if (trailing) {
      lastValue = new Promise((resolve, reject) => {
        lastRejector = rejectOnCancel ? reject : resolve;
        timer = setTimeout(() => {
          lastExec = Date.now();
          isLeading = true;
          resolve(invoke());
          clear();
        }, Math.max(0, duration - elapsed));
      });
    }

    if (!leading && !timer) timer = setTimeout(() => isLeading = true, duration);

    isLeading = false;
    return lastValue;
  };