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，但是有一个使用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();
});

我阅读了在承诺链中间的事件发射器的答案. 这给了我一种执行'connect'事件的回调的方法. 这是我到目前为止的去处

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
    });
});

现在如何进一步链接'eventB'?

Now how to chain further for 'eventB' ?

推荐答案

我假设您要为每个事件执行不同的操作.即使eventB是由connect的动作触发的，您也可以将其视为另一种逻辑流.

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.

侧面说明:为避免对您和其他必须阅读此代码库的人造成混淆，我建议不要用其他方法来补充Promise，除非您非常非常详尽地记录了它们.

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.

在您的示例中，似乎可以进行以下操作.

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()
})

如果您想简化此常量

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

您可以使用类似的东西

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了

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()
})

并且因为Javascript中的函数捕获了定义它们的范围，所以可以将该代码进一步简化为

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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