Learn ECMAScript - Second Edition

The __proto__ property

JavaScript objects have an internal [[prototype]] property that references the object's prototype, that is, the object it inherits: the prototypal inheritance model, which JavaScript uses. To read the property, we had to use Object.getPrototypeof() and to create a new object with a given prototype, we had to use the Object.create() method. A [[prototype]] property cannot be directly read or be modified.

Inheriting was cumbersome due to the nature of the [[prototype]] property; therefore, some browsers added a special __proto__ property in objects, which is an accessor property that exposes the internal [[prototype]] property and makes working with prototypes easier. The __proto__ property was not standardized in ES5, ...