当事件触发时触发 Promise [英] Trigger Promise when an event fires

问题描述

我的整个项目都使用 (Bluebird) Promises，但有一个使用 EventEmitter 的特定库.

My entire project uses (Bluebird) Promises, but there's one particular library that uses EventEmitter.

我想实现以下目标:

Promise.on('connect', function() {
    x.doSomething();
}).then(function() {
    return new Promise(function(resolve) {
        y.doAction(resolve); // this will result in `eventB` getting emitted
    });
}).on('eventB', function() {
    z.handleEventB();
}).then(function() {
    z.doSomethingElse();
});

我阅读了 位于承诺链中间的 EventEmitter 的答案.这给了我一种执行connect"事件回调的方法.这是我到目前为止的地方

I read the answer to EventEmitter in the middle of a chain of Promises. That gives me a way to execute the callback for 'connect' event. Here's where I have got so far

var p = new Promise(function(resolve) {
    emitter.on('connect', resolve);
});
p.on = function() {
    emitter.on.apply(emitter, arguments);
    return p;
};
p.on('connect', function() {
    x.doSomething();
}).then(function() {
    return new Promise(function(resolve) {
        y.doAction(resolve); // this will result in eventB getting emitted
    });
});

现在如何为 'eventB' 进一步链接?

Now how to chain further for 'eventB' ?

推荐答案

我假设您希望为每个事件做一系列不同的事情.即使 eventB 是由 connect 的动作触发的，你也可以把它当作另一个逻辑流.

I assume you want to do a different chain of things for each event. Even if eventB is triggered by the actions of connect, you can treat it like another stream of logic.

旁注:为了避免让您和其他任何必须阅读此代码库的人感到困惑，我建议您不要用其他方法补充 Promise，除非您非常完整地记录了它们.

Side note: To avoid confusion for you and anyone else who has to read this codebase, I'd recommend against supplementing promises with additional methods unless you are very thorough about documenting them.

从您的示例来看，以下内容似乎可行.

From your example, it seems like the following would work.

var Promise = require( 'bluebird' )
var emitter = someEmitter()
var connected = new Promise( function( resolve ){
    emitter.on( 'connect', resolve )
})

var eventBHappened = new Promise( function( resolve ){
    emitter.on( 'eventB', resolve )
})

connected.then( function(){
    return x.doSomething()
}).then( function(){
    return y.doSomethingElse() // will trigger `eventB` eventually
})

// this promise stream will begin once `eventB` has been triggered
eventBHappened.then( function(){ 
    return z.doSomething()
})

如果你想简化这个常量

var p = new Promise( function( resolve ){
    emitter.on( 'something', resolve )
})

你可以使用这样的东西

function waitForEvent( emitter, eventType ){
    return new Promise( function( resolve ){
        emitter.on( eventType, resolve )
    })
}

将上面的代码解决方案变成

Which turns the code solution above into

var Promise = require( 'bluebird' )
var emitter = someEmitter()

function waitForEvent( eventEmitter, eventType ){
    return new Promise( function( resolve ){
        eventEmitter.on( eventType, resolve )
    })
}

waitForEvent( emitter, 'connect' ).then( function(){
    return x.doSomething()
}).then( function(){
    return y.doSomethingElse() // will trigger `eventB` eventually
})

// this promise stream will begin once `eventB` has been triggered
waitForEvent( emitter, 'eventB' ).then( function(){ 
    return z.doSomething()
})

而且由于 Javascript 中的函数捕获了它们被定义的范围，所以这段代码可以进一步简化为

And because functions in Javascript capture the scope where they were defined, this code could be further simplified to

var Promise = require( 'bluebird' )
var emitter = someEmitter()

function waitForEvent( type ){
    return new Promise( function( resolve ){
        //emitter has been captured from line #2
        emitter.on( type, resolve ) 
    })
}

waitForEvent( 'connect' ).then( function(){
    return x.doSomething()
}).then( function(){
    return y.doSomethingElse() // will trigger `eventB` eventually
})

// this promise stream will begin once `eventB` has been triggered
waitForEvent( 'eventB' ).then( function(){ 
    return z.doSomething()
})

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