Handling functions that already return a promise ... ?

[dragoscirjan]

Hi,

I'm trying to write PromisedEventEmitter class based on your article Promisify event emitter.

On the em3 case, javascript throws me an error like TypeError: Object true has no method 'then' at Context. (test/PromisedEventEmitter.js:93:54). I guess it is because the function is already returning a promise.

Any idea on how to treat this case?

Many thanks in advance.

/**
 * Created by dragosc on 09.05.2015.
 */

var assert = require("assert")

//var em = new (require('../index').PromisedEventEmitter)
var events = require('events');
var selfAddressed = require('self-addressed');
var eventEmitter = new events.EventEmitter()
var fs = require('fs')
var Q = require('q')

describe('Array', function(){
    describe('#indexOf()', function(){
        it('should return -1 when the value is not present', function(){
            assert.equal(-1, [1,2,3].indexOf(5));
            assert.equal(-1, [1,2,3].indexOf(0));

            var _emit = events.EventEmitter.prototype.emit;
            eventEmitter.emit = function (name, data) {
                //function mailman(address, envelope) {
                //    return _emit.apply(address, [name, envelope]);
                //}
                var result = _emit.apply(this, [name, envelope])
                function mailman(address, envelope) {
                    return result;
                }
                return selfAddressed(mailman, this, data); // returns a promise
            };

            var _on = events.EventEmitter.prototype.on;
            eventEmitter.on = function (name, fn) {
                function onSelfAddressedEnvelope(envelope) {
                    if (selfAddressed.is(envelope)) {
                        var result = fn();
                        selfAddressed(envelope, result);
                        // there is nowhere to send the response envelope
                        // event emitters are unidirectional.
                        // so open the envelope right away!
                        envelope.replies = 1;
                        selfAddressed(envelope); // deliver
                    }
                }
                _on.apply(this, [name, onSelfAddressedEnvelope]);
            };

            var readFileSync = function(path) {
                var result = fs.readFileSync(path).toString();
                console.log('sync:')
                console.log(result)
                return result
            }

            var em = new events.EventEmitter()

            console.log('starting readFileSync event')
            em.on('readFileSync', readFileSync)
            console.log(
                em.emit('readFileSync', '/etc/resolv.conf')
            )
            console.log('ending readFileSync event')

            var em2 = new (require('../promised-events').QEventEmitter)

            console.log('starting Q readFileSync event')
            em2.on('readFileSync', readFileSync)
            em2.emit('readFileSync', '/etc/resolv.conf').then(function(result){
                console.log('THEN sync:')
                console.log(result)
            })
            console.log('ending Q readFileSync event')

            var readFile = function(path) {
                var defered = Q.defer()
                fs.readFile(path, function(err, data) {
                    if (!err) {
                        console.log('async:')
                        console.log(data.toString())
                        defered.resolve(data.toString())
                    } else {
                        defered.reject(err)
                    }
                })
                return defered.promise
            }

            //var em3 = new (require('../promised-events').PromisedEventEmitter)
            var em3 = new events.EventEmitter()

            console.log('starting Q readFile event')
            em3.on('readFile', readFile)
            em3.emit('readFile', '/etc/resolv.conf').then(function(result){
                console.log('THEN async:')
                console.log(result)
            })
            console.log('ending Q readFile event')

        })
    })
})

[bahmutov]

let me try running this unit test myself to see what is going on. Node 0.10 / 0.12 I assume?

[dragoscirjan]

Yes, it's node 0.10. Thank you for your support.

node --version
v0.10.25