ES6 Generator函数核心特性与异步编程实战详解

function * fn() {
 console.log('hello');
 return 'Joh';
}
// 执行fn()时不会直接执行方法体中的代码，它会返回一个指针, 这个指针实现了 interator接口，也就是返回一个interator对象
let it = fn();
// 通过调用next就会执行方法体, 返回结果是 {value:'Joh', done:true}, 其中next返回的是函数体中return的值
let res = it.next();
console.log(res);

function * fn() {
  // 和yield相配合，把一个generator内部分为几个断点来执行，每个断点就是yield语句
  // 注意 yield和return的区别： yield可以有多个，return只能有1个
  yield 1;
  yield 2;
  yield 3;
  return 4; // 可以没有return值，done为true的value将会是undefined
}
let it = fn();
// 在for-of 循环中只能打印done为false的value值，done为true时,程序终止
for(let v of it) {
  console.log(v); // 分别输出 1 2 3
}

function * fn(_name) {
 let name = yield _name; // yield 的默认值为undefined
 return name;
}
let it = fn('Joh');
console.log(it.next()); // {value:'Joh', done:false}
console.log(it.next('Tom')); // {value:'Tom', done:true} // 此处value应该为undefined，但是通过next参数的形式赋值改变了最后一个值
console.log(it.next('Lily')); // {value: undefined, done:true} // 已经循环完毕，即使传值也是undefined

function sum(a, b) {
 return a + b;
}
function * fn() {
 let res = sum(yield 1, 5 + (yield 3));
 console.log(res);
 console.log('my qq: ' + (yield qq)); // yield 在一个语句中需要括起来
}
fn();

function * fn() {
 let qq = yield; // yield 默认返回undefined, 不会抛出异常
 console.log(qq);
}
let g = fn();
g.next(); // 第一个断点没有输出
// g.next('qq 11111'); // 完毕之后传值输出：qq 11111
g.throw('error!'); // Uncaught error!

function * fn() {
 let qq;
 try {
  qq = yield; // yield 默认返回undefined
 }catch(e){
  console.log('qq have error');
 }finally{
  console.log(qq);
 }
}
let g = fn();
g.next();
g.throw('error!');
// qq have error
// undefined

function * fn() {
 let qq;
 qq = yield;
 console.log(qq);
}
let g = fn();
g.next();
try{
 g.throw('error!');
}catch(e){
 console.log('qq have error!');
}

function * fn() {
 let qq;
 try {
  qq = yield ff; // ff 未定义, 所以qq不会被正确赋值 此处是非 yield 的异常
 }catch(e){
  console.log('err1');
 }
 console.log(qq);
}
let g = fn();
g.next();
g.next('qq 5554');
// err1
// undefined

function asyncF(name) {
 return new Promise(function(resolve){
  setTimeout(function(){
   resolve('my name is ' + name);
  });
 });
}
function * fn() {
 console.log(yield asyncF('Joh'));
}
let gf = fn();
function exec(gf,value) {
 let res = gf.next(value);
 if(!res.done) {
  if(res.value instanceof Promise) {
   res.value.then(function (v) {
    exec(gf, v);
   })
  }else{
   exec(gf, res.value);
  }
 }
}
exec(gf); // my name is Joh

function asyncF(name) {
 return new Promise(function(resolve){
  setTimeout(function(){
   resolve('my name is ' + name);
  });
 });
}
function sum(a, b) {
 return new Promise(function (resolve) {
  setTimeout(function () {
    resolve(a + b);
  });
 })
}
function * fn(name) {
 if((yield sum(3,5)) > 6) {
  console.log(yield asyncF(name));
 }else{
  console.log('error');
 }
}
let gf = fn('Joh');
// generator 执行器 相当于 tj/co 模块
function exec(gf,value) {
 let res = gf.next(value);
 if(!res.done) {
  if(res.value instanceof Promise) {
   res.value.then(function (v) {
    exec(gf, v);
   })
  }else{
   exec(gf, res.value);
  }
 }
}
exec(gf); // my name is Joh

function asyncF(name) {
 return new Promise(function(resolve){
  setTimeout(function(){
   resolve('my name is ' + name);
  });
 });
}
function sum(a, b) {
 return new Promise(function (resolve) {
  setTimeout(function () {
    resolve(a + b);
  });
 })
}
function fn(name) {
 sum(3,5)
  .then(function (num) {
   if(num > 6) {
    asyncF(name)
     .then(function (v) {
      console.log(v);
     })
   }else{
    console.log('error');
   }
  })
}
fn('Joh');

var co = require('co');
function asyncF(name) {
 return new Promise(function(resolve){
  setTimeout(function(){
   resolve('my name is ' + name);
  });
 });
}
function sum(a, b) {
 return new Promise(function (resolve) {
  setTimeout(function () {
    resolve(a + b);
  });
 })
}
function * fn(name) {
 if((yield sum(3,5)) > 6) {
  console.log(yield asyncF(name));
 }else{
  console.log('error');
 }
}
var fnx = co.wrap(fn);
fnx('Joh'); // my name is Joh