如何区分箭头函数、类和普通函数? [英] How can I differentiate between an arrow function, class and a normal function?

问题描述

如何使用 ES6 中的引用来区分这三件事?

How can I differentiate between these three things in ES6 using its reference?

let x = i => i+1;

class y { constructor(i) { this._i=i+1; } get i(){ return this._i;} }

function z(i) { return i+1; }

示例:

test(x) //=> 'arrow'
test(y) //=> 'class'
test(z) //=> 'function'

我如何区分转译器中的这些东西 - Traceur/Babel?

And how can I differentiate between these things in transpilers - Traceur / Babel?

推荐答案

我如何区分 ES6 中的这些东西?

How can I differentiate between these things in ES6?

• 箭头函数是不能用作构造函数的函数，并且没有 .prototype 属性.但是，方法也不是.它们继承自 Function.prototype.
• 类是在没有 new 的情况下无法调用的函数，并且具有通常不为空的 .prototype 对象.如果使用了 extends 关键字，它们不会从 Function.prototype 继承.
• 函数是可以以任何一种方式调用的函数，并且确实具有 通常为空的 .prototype.它们继承自 Function.prototype.
• 生成器函数是具有 .prototype 的函数，它继承自内在的 GeneratorPrototype 对象，并且它们继承自内在的 Generator 对象.
• arrow functions are functions that cannot be used as constructors, and don't have a .prototype property. However, methods don't either. They inherit from Function.prototype.
• classes are functions that can't be called without new, and that have a .prototype object which is normally not empty. If the extends keyword was used, they don't inherit from Function.prototype.
• functions are functions that can be called either way, and do have a .prototype that is normally empty. They inherit from Function.prototype.
• generator functions are functions that do have a .prototype which inherits from the intrinsic GeneratorPrototype object, and they inherit from the intrinsic Generator object.

如您所见，有一些线索.然而，属性和继承总是会被弄乱，所以你不能真正信任它.一个函数是否是构造函数(可以用 new 调用)无法从外部确定，你必须调用它并查看它是否抛出 - 这也可以伪造.

As you can see, there are some clues. However, the properties and inheritance can always be messed with, so you cannot really trust it. Whether a function is a constructor (can be called with new) cannot be determined from outside, you have to call it and see whether it throws - which could be faked as well.

所以你最好的选择可能是 Function.prototype.toString，看看源代码是什么样的.如果您的 ES 实现支持这一点.

So your best bet might be Function.prototype.toString, to see how the source looked like. If your ES implementation supports that.

我如何区分转译器中的这些东西?

And how can I differentiate between these things in transpilers?

我认为没有任何转译器实现无原型的箭头和方法.类构造函数是否在被调用时抛出取决于转译的松散程度，但这无论如何都不是区分的好方法.
toString 也不能正常工作.

I don't think any transpiler implements prototype-less arrows and methods. Whether a class constructor throws upon being called depends on the looseness of the transpilation, but that's not a good way for distinction anyway.
toString doesn't work either afaik.

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