node.js - javascript: require('events').EventEmitter; - Stack Overflow

admin管理员组

文章数量:1357268

Why

var EventEmitter = require('events').EventEmitter;
var channel = new EventEmitter();

works, but

var EventEmitter = require('events');
var channel = new EventEmitter();

does not work! Actually, I have another totally different example,

var Currency = require('./currency)
var Cu = new Currency();

works, but

var Currency = require('./currency).Currency;
var Cu = new Currency();

does not work. Here is my currency.js:

function Currency(canadianDollar) {
    this.canadianDollar = canadianDollar;
}

module.exports = Currency;

Currency.prototype.cal = function(amount) {
    return amount * this.canadianDollar;
}

Why

var EventEmitter = require('events').EventEmitter;
var channel = new EventEmitter();

works, but

var EventEmitter = require('events');
var channel = new EventEmitter();

does not work! Actually, I have another totally different example,

var Currency = require('./currency)
var Cu = new Currency();

works, but

var Currency = require('./currency).Currency;
var Cu = new Currency();

does not work. Here is my currency.js:

function Currency(canadianDollar) {
    this.canadianDollar = canadianDollar;
}

module.exports = Currency;

Currency.prototype.cal = function(amount) {
    return amount * this.canadianDollar;
}

• javascript
• node.js
• eventemitter

Share Improve this question Follow asked Feb 4, 2014 at 16:04 BensonBenson 27522 gold badges66 silver badges1212 bronze badges 3

• Because they export different things. – SLaks Commented Feb 4, 2014 at 16:07
• github./joyent/node/blob/v0.10.22/lib/events.js#L38 – SLaks Commented Feb 4, 2014 at 16:08
• if you want yours to be like events, module.exports = {Currency:Currency}; – dandavis Commented Feb 4, 2014 at 16:08

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 8

Because this is the way the API is written. A simplified example of "events" module would look like:

module.exports = {
    EventEmitter: function () {
        // ...
    }
};

In the above case require('events'); would return an Object containing EventEmitter, but require('events').EventEmitter would return the actual EventEmitter function you are likely interested in instantiating.

Thought it would be good to mention that the API designer could indeed export the EventEmitter function directly with module.exports = function () { ... }; however, they decided to leave space for other potentially useful properties of the "events" module.

Edit

Regarding module.exports = EventEmitter; in https://github./joyent/node/blob/master/lib/events.js, on the following lines you can find:

// Backwards-pat with node 0.10.x
EventEmitter.EventEmitter = EventEmitter;

I suppose that starting from version 0.11 you can run var Emitter = require('events');, but in 0.10.x you are stuck with require('events').EventEmitter.

require returns exactly what you put in module.exports object. So if you have module.exports = Currency; then require returns Currency and if you have exports.Currency = Currency require will return { Currency : Currency } object.

if you want this to work both ways, just do Currency.Currency = Currency; module.exports = Currency. in latest node releases they do like this with EventEmitter

本文标签： nodejsjavascript require(39events39)EventEmitterStack Overflow