javascript - Node.js 无法读取未定义的属性 'on'

Question

怎么了？

附注: 我是 node.js 的新手，我来自 .Net 世界!

我的 server.js 代码:

    var events = require('events').EventEmitter;
    var v = function() {
        var e = new events();
        e.emit('start');
    };

    var r = v();
    r.on('start', function(){
        console.log('event start just fired!!!!!!!!!!');
    });

和这个控制台输出:

TypeError: Cannot read property 'on' of undefined
    at Object.<anonymous> (E:\Project\node\BasicSocial\server.js:12:2)
    at Module._compile (module.js:410:26)
    at Object.Module._extensions..js (module.js:417:10)
    at Module.load (module.js:344:32)
    at Function.Module._load (module.js:301:12)
    at Function.Module.runMain (module.js:442:10)
    at startup (node.js:136:18)
    at node.js:966:3

Answer 1

您忘记从您的 v 函数返回事件发射器:

var v = function() {
    var e = new events();
    e.emit('start');
    return e;
};

另请注意，start 事件将不会被调用，因为您在订阅它之前已经发出了该事件。所以你可以稍微修改一下你的代码:

var events = require('events').EventEmitter;
var v = function() {
    var e = new events();
    return e;
};

var r = v();
r.on('start', function(){
    console.log('event start just fired!!!!!!!!!!');
});

// emit the event after you have subscribed to the start callback
r.emit('start');