_proto_ is simply a way to access the internal ] in some JS environments. This means that _proto_ and ] refer to the same thing. At some point, however, browser vendors and other environments started giving access to the internal ] object via the _proto_ property. Since ] is an internal property it was never meant to be accessible by developers, according to the ECMA specs. Further, even function constructors have an internal ]. This goes for for objects created with object literals, those created with the new keyword and also for those created with Object.create(). ] is an internal property on all JS objects that points to the object's prototype. This means that those internal properties are not accessible by the objects that contain them. In the ECMAScript specifications double brackets denote internal properties and are, according to the specs, not part of the ECMAScript language. This article is an overview and explanation of the different kinds of prototypes and their purposes in JavaScript.

If you have ever been confused about all the different kinds of prototypes in JavaScript, you are not alone. It can be accessed via the _proto_ property.prototype is an object which exists only on function constructors and is used to set a constructed object's internal ] TL DR: ] is an internal property that exists on all JS objects.

What is prototype in javascript