“new< function>”之后的括号可选的？ [英] Parentheses after "new <function>" optional?

问题描述

我在Chrome控制台中运行了以下一对代码段，结果相同：

I have run the following pair of code snippets in Chrome console, with the same results:

test = new function(){
  var a = 1;
  var b = 2;
  var c = 3;
  this.debugBase = function(){console.log('' + a + b + c)};
};
test
debugBase: function (){console.log('' + a + b + c)}
__proto__: Object

对比：

test2 = new (function(){
  var a = 1;
  var b = 2;
  var c = 3;
  this.debugBase = function(){console.log('' + a + b + c)};
})();
test2
debugBase: function (){console.log('' + a + b + c)}
__proto__: Object

我错过了什么吗？函数后的括号有什么意义吗？如果没有，人们为什么要把它们放在那里？

Am I missing something? Is there any significance to the parentheses after the function? If not, why do people put them there?

推荐答案

这里提出了类似的问题：新MyClass（）与新MyClass 。 Daniel Vassallo完整且接受的答案：

A similar questions was asked here: new MyClass() vs. new MyClass. The complete and accepted answer by Daniel Vassallo:

引用 David Flanagan ¹ ：

作为一个特殊的例如，对于 new 运算符，JavaScript通过允许在函数调用中没有参数时省略括号来简化语法。以下是使用 new 运算符的一些示例：

As a special case, for the new operator only, JavaScript simplifies the grammar by allowing the parenthesis to be omitted if there are no arguments in the function call. Here are some examples using the new operator:

o = new Object;  // Optional parenthesis omitted here
d = new Date();  

---

就个人而言，我总是使用括号，即使构造函数没有参数。

---

Personally, I always use the parenthesis, even when the constructor takes no arguments.

此外， JSLint 可能会伤害您的感受如果省略括号。它报告 Missing'（）'调用构造函数，并且似乎没有工具允许括号省略的选项。

In addition, JSLint may hurt your feelings if you omit the parenthesis. It reports Missing '()' invoking a constructor, and there doesn't seem to be an option for the tool to tolerate parenthesis omission.

¹ David Flanagan： JavaScript权威指南：第4版（第75页）

¹ David Flanagan: JavaScript the Definitive Guide: 4th Edition (page 75)

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