L2L 2L wrote:
I see the value of this, cause it denote not only the constructor, but what an
object is:
Object.getConstructorOf("")//String
Object.getConstructorOf(0)//Number
Object.getConstructorOf(function(){})//Function
Object.getConstructorOf({})//Object
Object.getConstructorOf([]);//Array
If you try the first to with Object.getPrototypeOf("");
Object.getPrototypeOf(0);
You'll get an error message, cause primitive value don't have prototype. But
they do have wrapper objects; constructor objects.
This to me is a needed feature of the language.
It's not a "kernel language" feature, as you showed -- it is library
code that can be built on top of the core language. And you are right
that we seem to observe a fair amount of
Object.prototype.toString.call(x).slice(8, -1)
for value x.
However, getConstructorOf("") returning "String" (a string value),
instead of the constructor function, is misleading. But returning the
constructor function reference is wrong for primitive values, because 42
!== new (42).constructor(42). Primitives have value not reference semantics.
What you are really proposing is an Object.getToStringTag method. But in
ES6, that is just x[Symbol.toStringTag], if I'm not mistaken. So do we
really need Object.getToStringTag(x), which is longer?
See
http://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.prototype.tostring
for the ES6 spec.
Then you could argue that an Object "static method" is better both to
hide the Symbol.toStringTag detail and to enable polyfilling on pre-ES6
browsers. That's a fair point.
/be
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