那么可不可以优化一下呢？写成一行要注意，因为使用了逗号，避免被认为是函数的参数分割，导致 yes 不被调用，可以加一个括号括起来。最外层的也可以写成一行，外层真写成一行，那就过分了。

  1. function ready() {
  2.   let resolveFN, rejectFN
  3.   let promise = new Promise(
  4.     (resolve, reject) => ([resolveFN, rejectFN] = [resolve, reject])
  5.   )
  6.   return [resolveFN, rejectFN, promise]
  7. }
  9. // 保存文件
  10. const saveFile = (path, data) => {
  11.   const [yes, no, wait] = ready()
  12.   jsonfile.writeFile(path, data, e => (e && no(e), yes()))
  13.   return wait
  14. }
  16. const sleep = time => {
  18.   return wait
  19. }
  21. const exits = path => {
  22.   const [yes, no, wait] = ready()
  23.   fs.stat(path, (e, stats) => (e && no(e), yes(stats)))
  24.   return wait
  25. }
  27. const ensureSavaPath = path => exits(path).catch(() => mkdir(path))

那么继续抽象的话，其实对于这种 node 统一风格的非常容器转换成 promise，使用 promisify 即可，类似于 Rxjs 的 bindNodeCallback 。

  1. const { promisify } = require('util')
  3. function ready() {
  4.   let resolveFN, rejectFN
  5.   let promise = new Promise(
  6.     (resolve, reject) => ([resolveFN, rejectFN] = [resolve, reject])
  7.   )
  10. const sleep = time => {
  11.   const [yes, no, wait] = ready()
  12.   setTimeout(yes, time)
  13.   return wait
  14. }
  16. // 保存文件
  17. const saveFile = promisify(jsonfile.writeFile)
  19. const exits = promisify(fs.stat)
  21. const ensureSavaPath = path => exits(path).catch(() => mkdir(path))

核心逻辑

当下载内容时候，同样适用 craw 提供的爬取内容的规则。

  1. async function downloadText(chapter, crawl, index, opts) {
  2.   const { path, charset } = opts
  3.   const selector = await buildSelector(chapter.url, charset)
  4.   const text = crawl.text(selector)
  6. }