lei-mu / single-promises Goto Github PK

import {version} from '../package.json'



/**
 * 用于包装一个函数并返回一个新函数，使其调用这个新函数只有一个promise在执行，后续的调用都会返回这个promise
 * @param fn {function(...[*]): (Promise<Awaited<*>>)} - 需要包装的函数
 * @param opt {object} - 配置项
 * @param opt.cache {number} [opt.cache = 0] - 缓存时间，单位毫秒，如果大于0，则会缓存结果，下次调用如何结果仍在有效缓存时间内，则会直接返回缓存的结果。默认0，不缓存
 * @return {(function(...[*]): (Promise<Awaited<*>>))|*}
 */
  function singlePromise(fn, opt = {}) {
    const defaultOpt = {
    cache: 0
    }
    let promise
    let cacheMill = -1
    let cacheRes

  opt = Object.assign({}, defaultOpt, opt)

  function handle(...args) {
    let self = this
    let {cache} = opt

    if (cache && cacheMill > 0) {
      if (Date.now() - cacheMill < cache) {
        return Promise.resolve(cacheRes)
      } else {
        cacheMill = -1
        cacheRes = null
      }
    }
    if (promise) {
      return promise
    } else {
      promise = Promise.resolve(fn.apply(self, args))
    }
    return promise.then((res) => {
      if (cache) {
        cacheMill = Date.now()
        cacheRes = res
      }
      promise = null
      return res
    }).catch((err) => {
      promise = null
      return Promise.reject(err)
    })
  }

  handle.clear = function () {
    cacheMill = -1
    cacheRes = null

  }
  handle.update = function (newOpt = {}) {
    opt = Object.assign({}, opt, newOpt)
  }

  return handle

}

export {
  singlePromise,
  version
}

const getTime = (t) => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(Date.now() * t)
    }, 1000)
  })
}
const singleOptions = {
  cache: 0
}


const singleGetTime = singlePromise(getTime, singleOptions)

for (let i = 0; i < 5; i++) {
  // 希望调用 时能有参数提示，参数同getTime
  singleGetTime(3).then((res) => {
    console.log('res', res)
  })
}
// 希望能有 clear 方法提示
singleGetTime.clear()
const newSingleOptions = {
  cache: 1
}
// 希望能有 update 方法提示、参数提示
singleGetTime.update(newSingleOptions)


// fn 支持同步函数。
const getTime2 = (str) => {
  return Date.now() + str
}

// fn 可以是同步函数，但singlePromise 函数返回的函数，调用时永远返回promise
const singleGetTime2 = singlePromise(getTime2)