详解ES6中的三种异步解决方案

const fs = require('fs')

// Promise 版的readFile
const readFile = function (fileName) {
 return new Promise(function(resolve, reject) {
  fs.readFile(fileName, function(err, data){
   if (err) return reject(error);
   resolve(data);
  })
 })
}

const gen = function * () {
 let f1 = yield readFile('a.txt');
 let f2 = yield readFile('b.txt');

 console.log('F1--->', f1.toString());
 console.log('F2--->', f2.toString());
}


// 基于 Generator 和 Promise 的自动执行器
function run(gen) {

 let g = gen();
 
 function next(data) {
  
  let result = g.next(data);

  if (result.done) return result.value;

  result.value.then(function(data) {
   next(data);
  });
 }
 next();
}

run(gen);

const fs = require('fs')

// 把一个单一执行的函数 ，变成需要再次调用的函数，固定一部分参数
function thunkify(fn, obj = {}) {
  return function () {
    let args = Array.from(arguments);
    return function (m) {
      args.push(m)
      return fn.apply(obj, args)
    }
  }
}

const readFile = thunkify(fs.readFile, fs);

const gen = function* () {
  let f1 = yield readFile('a.txt');
  let f2 = yield readFile('b.txt');

  console.log('F1-->', f1.toString());
  console.log('F2-->', f2.toString());
}


// 基于 Generator 和 Thunk函数的自动执行器
function run(fn) {
  let gen = fn();

  function next(err, data) {
    let result = gen.next(data);
    if (result.done) return 1;
    result.value(next);
  }

  next();

}

run(gen);

const fs = require('fs')

// Promise 版的readFile
const readFile = function (fileName) {
 return new Promise(function(resolve, reject) {
  fs.readFile(fileName, function(err, data){
   if (err) return reject(err);
   resolve(data);
  })
 })
}

const asyncReadFile = async function () {
 const f1 = await readFile('a.txt');
 const f2 = await readFile('b.txt');
 console.log(f1.toString());
 console.log(f2.toString());
};

asyncReadFile();