要求如何与Node.js中的新运算符一起使用? [英] How does require work with new operator in node.js?

问题描述

让我们用以下代码创建一个file.js:

Let's have a file.js with this code:

module.exports.func = function(txt) {
    this.a = 1;
    this.b = 2;
    console.log(txt, this);
    return this;
}

现在我们有另一个JS文件，我们在其中执行以下操作:

Now we have another JS file where we do following:

var r1 = new (require('./file')).func('r1');
var r2 = new require('./file').func('r2');

在r1情况下，它可以按预期工作-r1包含对新创建对象的引用.

In r1 case it works as intended - r1 contains reference to the newly created object.

在r2情况下，它不起作用-r2从file.js中获取对module.exports的引用.

In r2 case it does not work - r2 gets reference to module.exports from within the file.js.

目的是通过调用func()构造函数来创建一个新对象.当然，我也可以用等于r1的方式来做到这一点:

The intention was to create a new object by calling func() constructor. Sure, I can do it also this way which is equal to r1:

var r3 = require('./file');
var r4 = new r3.func('r1');

但是，我不明白为什么r2的行为方式与r1不同.

However, I do not understand why r2 does not behave the same way as r1.

require('./file')周围的多余括号如何产生作用?

How do the extra parenthesis around require('./file') make a difference?

推荐答案

这两个版本根本不同.

这个:

new (require('./file')).func('r1');

执行require，返回./file的导出，然后对结果调用新的运算符 .

Executes the require, returning the exports of ./file and then calling the new operator on the results .

这个:

var r2 = new require('./file').func('r2');

调用需要作为构造函数.

Invokes require as a constructor.

让我们看一个更孤立和简单的示例:

Let's look at a more isolated and simple example:

new Date() // creates a new date object
new (Date()) // throws a TypeError: string is not a function

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