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I was playing with class/function/prototype inheritance a bit and got a decent setup working. Something simple that I understand.

http://jsfiddle.net/rudiedirkx/rwPeD/6/

For debugging purposes, I wanted to print in each constructor what kind of object was calling that constructor. For instance the Ronin constructor calls the Ninja constructor and that calls the Person constructor. For that I made a get_class function:

function get_class(obj) {
    var C = String(obj.__proto__.constructor);
    return C.match(/function (\w+)\(/, C)[1];
}

and that doesn't work. It always returns "Person". Why? Every 'class' has its own constructor, doesn't it? If I do a console.log(this) in every constructor, Chrome Devtools knows which type the object is. How do I get there (with vanilla JS)?

PS. Full output in my Chrome:

Chrome Devtools output

Rudie
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  • possible duplicate of [Why do you need to reset javascript constructor during inheritance?](http://stackoverflow.com/questions/13222696/why-do-you-need-to-reset-javascript-constructor-during-inheritance) – Bergi Jan 01 '14 at 14:20

2 Answers2

6

Or you could do something that actually works...

function getClass(obj) {
    return obj.__proto__.constructor.name;
}

obj.attr("class") only works if the method attr exists with it won't in a native environment.

Still your suggestion was very good in it's design.

Please note that proto.constructor.name will always return "Object" if the class is not a native class, such as Array, String, RegExp, Error, etc... If anyone knows how to convince the "name" property to return the real name, even if I have to add code to do it, I would buy him a banana for his/her trouble.

Erich Horn
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  • If `obj.__proto__.constructor` always returns the `Person` constructor, so will `obj.__proto__.constructor.name` always return "Person"... This is the exact same method I tried and that's not it. If it works for you, can you implement it in http://jsfiddle.net/rudiedirkx/rwPeD/6/ ? Thanks – Rudie Jul 18 '12 at 12:36
  • doesn't work when scripts are dynamically loaded (for example with require.js) – catbadger Jul 07 '16 at 15:39
  • error message: this.__proto__.constructor.name is not a function – Blessed Geek Mar 17 '17 at 23:46
  • To make this answer a little more "proper," you can replace `obj.__proto__` with `Object.getPrototypeOf(obj)`. See https://stackoverflow.com/a/22667193/1186756 – mopo922 Feb 13 '20 at 14:26
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    BEWARE: Logic based on this can break when your code is minified for production. When the value is "MyClassName" during development, it can be truncated simply to "e" when minified. – mopo922 Mar 02 '20 at 15:54
0

I think the problem refers to following line. this.prototype.constructor points to what Person.prototype points to.

this.prototype = Object.create(sup.prototype);

You may need change its reference explicitly.

this.prototype.constructor = this;

The similar question can be found at Get name of derived constructor in Javascript

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ucdream
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