Object.getPrototypeOf()

The Object.getPrototypeOf() method returns the prototype (i.e. the value of the internal [[Prototype]] property) of the specified object.

Object.getPrototypeOf(obj)

obj

The object whose prototype is to be returned.

The prototype of the given object. If there are no inherited properties, null is returned.

var proto = {};
var obj = Object.create(proto);
Object.getPrototypeOf(obj) === proto; // true

In ES5, it will throw a TypeError exception if the obj parameter isn't an object. In ES2015, the parameter will be coerced to an Object.

Object.getPrototypeOf('foo');
// TypeError: "foo" is not an object (ES5 code)
Object.getPrototypeOf('foo');
// String.prototype                  (ES2015 code)

Even though older Opera versions don't support Object.getPrototypeOf() yet, Opera supports the non-standard __proto__ property since Opera 10.50.

• Object.prototype.isPrototypeOf()
• Object.setPrototypeOf()
• Object.prototype.__proto__
• John Resig's post on getPrototypeOf
• Reflect.getPrototypeOf()