nodejs:继承EventEmitter

Question

我无法创建继承自EventEmitter的类。函数的结果是未定义。下面是一个简化的问题摘录：

var EventEmitter = require( 'events' );
var util = require( 'util' );
var zWave = require('./zWaveRequest.js');
var CronJobManager = require( 'cron-job-manager' );
var timespanToCron = require( './parseTime.js' ).timespanToCron;
var winston = require( './logger.js' );

const levelCronName = 'level';

var Switch = function (id, displayName, onTime, offTime) {
    var _nodeNum;
    var _nodeName;
    var _lastLevel = -1;
    var _levelPollInterval = config.levelPollInterval;
    var _levelTS = 0;
    var _cronMgr = new CronJobManager( );

    EventEmitter.call( this );

    var self = this;

    function initLevelJob() {
        // the log shows self.emit() doesn't exist (???)
        if( typeof self.emit === 'function' ) winston.info( 'initLevelJob(): self.emit() is defined' );
        else winston.info( 'initLevelJob(): self.emit() is NOT defined' );

        _cronMgr.add( levelCronName, timespanToCron( _levelPollInterval ), function() {
            self.getLevel();
        }, 
        {
            start: true,
        } );
    }

    this.getLevel = function() {
        zWave.curLevel( _nodeNum )
        .then( function( value ) {
            _lastLevel = value;
            _levelTS = Date.now( );

            // this next call always fails with an 'emit is not a function' error
            self.emit( 'level', self.lastLevel, self.lastLevelTS );
        } );
    }

    Object.defineProperties(this, {
        nodeNumber: {
            get: function() { return _nodeNum; },
            set: function( val ) {
                _nodeNum = val;
                initLevelJob( );
            },
        },

        levelPollInterval: {
            get: function() { return _levelPollInterval; },
            set: function( val ) {
                _levelPollInterval = val;
                initLevelJob( );
            }
        },
}

util.inherits( Switch, EventEmitter );

module.exports = Switch;

这里的总体想法是将cronjob设置为ping另一个服务器以获取信息(即对zWave的调用)。cronjob回调更新一些内部变量，然后发出一个事件。

但是self.emit()是未定义的，尽管我认为我遵循的是如何从EventEmitter继承的示例。

调用代码

从我现在如何使用emit()的角度来看，开关对象之外什么都不会发生。换句话说，我还没有将任何事件侦听器绑定到开关中。

下面是我如何创建交换机实例(SunsetSwitch是从交换机派生的)：

function createSwitch( switchFile ) {
    var raw = JSON.parse( fs.readFileSync( switchFile ) );
    var retVal;

    if( typeof raw.onTime === 'undefined' ) {
        // sunset switch
        retVal = new SunsetSwitch( );

        if( config.forceImmediateOn ) {
            var now = new Date( );

            var sunset = sunCalc.getTimes( now, config.latitude, config.longitude ).sunset;
            retVal.onOffset = Math.ceil( ( now - sunset ) / 60000 ) - 5;

            var turnOff = new Date( now );
            turnOff.setMinutes( now.getMinutes( ) + config.testMode.duration.totalMinutes() );
            retVal.offTime = turnOff;

            retVal.basedOnSunrise = raw.basedOnSunrise;
        }
        else {
            retVal.onOffset = raw.onOffset;
            retVal.offTime = raw.offTime;
            retVal.basedOnSunrise = raw.basedOnSunrise;
        }
    }
    else {
        // regular switch
        retVal = new Switch( );

        retVal.offTime = raw.offTime;
        retVal.onTime = raw.onTime;
    }

    if( config.forceImmediateOn ) retVal.ignoreInitialOff = false;
    else {
        if( typeof raw.ignoreInitial != 'boolean' ) retVal.ignoreInitialOff = true;
        else retVal.ignoreInitialOff = raw.ignoreInitialOff;
    }

    retVal.displayName = raw.displayName;
    retVal.nodeName = raw.nodeName;
    retVal.nodeNumber = raw.nodeNumber;

    return retVal;
}

createSwitch()是从读取一堆json文件的文件系统循环中调用的：

fs.readdirSync('./switches')
.filter(function (file) {
    return file.substr(-5) === '.json';
})
.forEach(function (file) {
    switches.push(createSwitch('./switches/' + file));
});

下面是我目前收到的错误消息：

未处理的拒绝(/home/mark/XmasLights/node_modules/bluebird/js/release/util.js:11:23)：self.emit不是在/home/mark/XmasLights/Swit.js:65:18 at tryCatcher self.emit at Promise._settlePromiseFromHandler (/home/mark/XmasLights/node_modules/bluebird/js/release/promise.js:488:31) at Promise._settlePromise (/home/mark/XmasLights/node_modules/bluebird/js/release/(/home/mark/XmasLights/node_modules/bluebird/js/release/promise.js:590:10) at Promise._settlePromises (/home/mark/XmasLights/node_modules/bluebird/js/release/promise.js:673:18) at Async._drainQueue (/home/mark/XmasLights/node_modules/bluebird/js/release/async.js:125:16) at Async._drainQueues (/home/mark/XmasLights/node_modules/bluebird/js/release/async.js:135:10) at Immediate.Async.drainQueues onImmediate at processImmediate immediateCallback

以下是如何定义SunsetSwitch的摘录：

var Switch = require('./switch.js');

var SunsetSwitch = function (id, displayName, onOffset, offTime) {
    Switch.call(this, id, displayName, null, offTime);
}

module.exports = SunsetSwitch;

Answer 1

感谢所有回应的人，特别是jfriend00，他们让我找到了解决方案的道路。

这个问题源于我在定义SunsetSwitch时没有做的一些事情，这是从交换机派生出来的。

我忽略了在SunsetSwitch的模块文件中包括这一行：

util.inherits( SunsetSwitch, Switch );

基于我对javascript的有限理解，这一遗漏阻止了原型被传播到SunsetSwitch。

我需要记住，在javascript中定义继承树并不像在C#中那样简单，因为我在这里积累了大部分经验。您必须同时设置属性-- Switch.call(this，id，displayName，null，offTime) --并复制原型-- util.inherits( SunsetSwitch，Switch )。