es6 co generator

es6-generator-co.js

// demo #1
var co = require('co');

function printTime() {
	"use strict";
	return '[' + Date.now() + '] ';
}

co(function* () {
	"use strict";

	var a = new Promise(function (resolve, reject) {
		setTimeout(function () {
			console.log(printTime() + 'a done. ');
			resolve('abc');
		}, 1000);
	});

	var b = new Promise(function (resolve, reject) {
		setTimeout(function () {
			console.log(printTime() + 'b done.  ');
			resolve('def');
		}, 2000);
	});

	var c = new Promise(function (resolve, reject) {
		setTimeout(function () {
			console.log(printTime() + 'c done.  ');
			resolve('pkq');
		}, 3000);
	});

	console.log(printTime() + 'start...');

	var aValue = yield a;
	console.log(printTime() + 'a yielded' + ' - ' + aValue);

	var bValue = yield b;
	console.log(printTime() + 'b yielded' + ' - ' + bValue);
	
	var cValue = yield c;
	console.log(printTime() + 'c yielded' + ' - ' + cValue);
})
	.then(function () {
		"use strict";
		console.log(printTime() + 'co end');
	})
	.catch(function (e) {
		"use strict";
		console.error(e);
	});
	
/* demo #1 result: 
/usr/local/bin/node --harmony co-test.js
[1428654896938] start...
[1428654897929] a done. 
[1428654897931] a yielded - abc
[1428654898928] b done.  
[1428654898928] b yielded - def
[1428654899928] c done.  
[1428654899928] c yielded - pkq
[1428654899929] co end

Process finished with exit code 0
 */

// demo #2，把 a 和 c 的延时时长对调
var co = require('co');

function printTime() {
	"use strict";
	return '[' + Date.now() + '] ';
}

co(function* () {
	"use strict";

	var a = new Promise(function (resolve, reject) {
		setTimeout(function () {
			console.log(printTime() + 'a done. ');
			resolve('abc');
		}, 3000);
	});

	var b = new Promise(function (resolve, reject) {
		setTimeout(function () {
			console.log(printTime() + 'b done.  ');
			resolve('def');
		}, 2000);
	});

	var c = new Promise(function (resolve, reject) {
		setTimeout(function () {
			console.log(printTime() + 'c done.  ');
			resolve('pkq');
		}, 1000);
	});

	console.log(printTime() + 'start...');

	var aValue = yield a;
	console.log(printTime() + 'a yielded' + ' - ' + aValue);

	var bValue = yield b;
	console.log(printTime() + 'b yielded' + ' - ' + bValue);

	var cValue = yield c;
	console.log(printTime() + 'c yielded' + ' - ' + cValue);
})
	.then(function () {
		"use strict";
		console.log(printTime() + 'co end');
	})
	.catch(function (e) {
		"use strict";
		console.error(e);
	});
	
/*
/usr/local/bin/node --harmony co-test.js
[1428654987498] start...
[1428654988482] c done.  
[1428654989480] b done.  
[1428654990478] a done. 
[1428654990478] a yielded - abc
[1428654990478] b yielded - def
[1428654990478] c yielded - pkq
[1428654990479] co end

Process finished with exit code 0
 */

demo #1 中，a, b, c 3 个 Promise 看上去完美滴“同步阻塞”地执行了；
demo #2 中，为何是 a、b、c 3 个 Promise 执行完之后才执行三条 console.log(printTime() + '...') 语句呢？

貌似是被 console 给骗了。。。debug 跟着执行可以看出 demo #2 实际上的执行流：

/usr/local/bin/node --debug-brk=53885 --nolazy --harmony co-test.js
Debugger listening on port 53885
[1428656786806] start...
[1428656786809] a done. 
[1428656787820] a yielded - abc
[1428656791926] b done.  
[1428656792936] b yielded - def
[1428656795012] c done.  
[1428656796025] c yielded - pkq
[1428656797039] co end