使用`new`和`（）`with require [英] using `new` and `()` with require

问题描述

有什么区别

var events  = require('events'),
    emitter = new events.EventEmitter();

和

var emitter = require('events').EventEmitter;

或 EventEmitter 在使用/时非常宽容不使用新和（）？

or EventEmitter is pretty forgiving in using/not using new and ()?

推荐答案

你的第二个例子根本没有调用 EventEmitter 。 emitter 最终成为对函数的引用，而不是通过调用它创建的对象。

Your second example doesn't call EventEmitter at all. emitter ends up being a reference to the function, not an object created by calling it.

如果你想要拥有（）：

var events  = require('events'),
    emitter = new events.EventEmitter();

vs

var emitter = require('events').EventEmitter();
// Note ------------------------------------^^

然后有两点不同：

1. 你有一个 events 对象引用事件模块。

你没有'调用 EventEmitter 时，请使用 new 。

You didn't use new when calling EventEmitter.

如果结果发射器相同，那么是的，这意味着 EventEmitter 故意使 new 可选。我在文档中看不到，所以我不知道我d依赖它。

If the resulting emitter is identical, then yes, it means that EventEmitter intentionally makes new optional. I don't see that in the docs, so I don't know that I'd rely on it.

...或 EventEmitter 在使用/不使用 new 和（）时非常宽容？

...or EventEmitter is pretty forgiving in using/not using new and ()?

最后一部分表明你使用了第三种选择：

The last part of that suggests you've used a third option:

var emitter = new require('events').EventEmitter;
// `new` -----^   but no () --------------------^

拥有（）可选不存在 EventEmitter 确实;这是执行它的JavaScript new 运算符：如果没有参数传递给构造函数，（）在 new 表达式中是可选的。 new 总是调用你给它的函数，无论是否有（） 。

Having () optional there isn't something EventEmitter does; it's the JavaScript new operator that's doing it: If you have no arguments to pass to the constructor function, the () are optional in a new expression. new always calls the function you give it, whether there are () there or not.

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