JS两种同步写异步的方法

async/await

https://javascript.info/async-await

需要浏览器支持，后者使用webpack转换为ES5.

There’s a special syntax to work with promises in a more comfortable fashion, called “async/await”. It’s surprisingly easy to understand and use.

Async functions

Let’s start with the async keyword. It can be placed before a function, like this:

async function f() {
  return 1;
}

The word “async” before a function means one simple thing: a function always returns a promise. Other values are wrapped in a resolved promise automatically.

For instance, this function returns a resolved promise with the result of 1; let’s test it:

 

async function f() {
  return 1;
}

f().then(alert); // 1

…We could explicitly return a promise, which would be the same:

 

async function f() {
  return Promise.resolve(1);
}

f().then(alert); // 1

So, async ensures that the function returns a promise, and wraps non-promises in it. Simple enough, right? But not only that. There’s another keyword, await, that works only inside async functions, and it’s pretty cool.

Bluebirds-coroutine

http://bluebirdjs.com/docs/api/promise.coroutine.html

具有跨浏览器支持性，不需要使用webpack进行翻译。

实际上Node环境也支持。

Promise.coroutine(GeneratorFunction(...arguments) generatorFunction, Object options) -> function

Returns a function that can use yield to yield promises. Control is returned back to the generator when the yielded promise settles. This can lead to less verbose code when doing lots of sequential async calls with minimal processing in between. Requires node.js 0.12+, io.js 1.0+ or Google Chrome 40+.

var Promise = require("bluebird");

function PingPong() {

}

PingPong.prototype.ping = Promise.coroutine(function* (val) {
    console.log("Ping?", val);
    yield Promise.delay(500);
    this.pong(val+1);
});

PingPong.prototype.pong = Promise.coroutine(function* (val) {
    console.log("Pong!", val);
    yield Promise.delay(500);
    this.ping(val+1);
});

var a = new PingPong();
a.ping(0);

Running the example:

$ node test.js
Ping? 0
Pong! 1
Ping? 2
Pong! 3
Ping? 4
Pong! 5
Ping? 6
Pong! 7
Ping? 8
...