A Question Regarding "util.inherits"

[BastiDood]

• Version: v10.2.1 (Current)
• Platform: 64-bit Windows 10 v1803 (OS Build 17134.81)
• Subsystem: util

Attached below is the permalink of the code for the inherits method of the util module.

node/lib/util.js

Lines 1170 to 1184 in 39f2096

	function inherits(ctor, superCtor) {
	if (ctor === undefined || ctor === null)
	throw new ERR_INVALID_ARG_TYPE('ctor', 'Function', ctor);
	if (superCtor === undefined || superCtor === null)
	throw new ERR_INVALID_ARG_TYPE('superCtor', 'Function', superCtor);
	if (superCtor.prototype === undefined) {
	throw new ERR_INVALID_ARG_TYPE('superCtor.prototype',
	'Function', superCtor.prototype);
	}
	ctor.super_ = superCtor;
	Object.setPrototypeOf(ctor.prototype, superCtor.prototype);
	}

As of opening this issue, line 1183 baffles my mind. Why would Node.js use Object.setPrototypeOf to set the prototypes of the classes/objects? I have heard from MDN that Object.setPrototypeOf is slower and less efficient than if one had just done this instead:

ctor.prototype = Object.create(superCtor.prototype);

Although the performance change is insignificant, I still believe that this proposal must be made. Thanks!

[devsnek]

its actually setting the prototype of the prototype of the ctor, not the prototype of the ctor. the other way to do that would be ctor.prototype.__proto__ = Object.create(superCtor.prototype) and Object.setPrototypeOf is just a better way of doing that. either way its replacing the prototype which means the engine has to reoptimise everything.

[BastiDood]

If it's not too much to ask, why does one have to set the prototype of the prototype of the inheriting object? I'm still learning the ropes of JavaScript, so I'd love to learn as much as I can.

[benjamingr]

It used to work this way, but there was a bug with making it work with ES2015 classes (which don't allow setting .prototype which doing this fixed.

See relevant changes here: 29da8cf

Here is the relevant bug #3452

[BastiDood]

Oh, I see now. Thanks for the clarification! I appreciate it.