Which method is used to get the prototype of an object?

The method used to get an object’s prototype is Object.getPrototypeOf().

In JavaScript, every ordinary object has an internal [[Prototype]] reference, which links it to another object in the prototype chain or to null. Object.getPrototypeOf(object) reads that reference and returns the actual prototype. For example, Object.getPrototypeOf([]) is Array.prototype, while Object.getPrototypeOf(Object.prototype) is null.

Several similarly named choices cause confusion. __proto__ can expose the same relationship through a legacy accessor, but it is discouraged in modern code. prototype is usually a property of constructor functions; it is the object assigned as the prototype of instances created with new, not a general method for reading an existing object’s prototype. Object.setPrototypeOf() changes a prototype rather than retrieving one.

Reflect.getPrototypeOf() is the closely related Reflect API equivalent. Object.getPrototypeOf() has been standardized since ECMAScript 5 and is the conventional answer for this question.