JS: Prototypes

In addition to their own properties, almost all JavaScript objects also have a prototype. A prototype is another object that is used as a fallback source of properties. The ancestral prototype, the entity behind all objects, is Object.prototype.

Many objects don’t directly have Object.prototype as their prototype, but instead have another object, which provides its own default properties. Such a prototype object will itself have a prototype, often Object.prototype, so that it still indirectly provides methods like toString. Functions derive from Function.prototype and arrays derive from Array.prototype.

var empty = {}
console.log(empty.toString)     // -> function toString()...{}
console.log(empty.toString())   // -> [object Object]

Object.getPrototypeOf function returns the prototype of an object. You can use Object.create to create an object with a specific prototype.

var protoRabbit = {
  speak: () => {
    console.log("I am Proto Rabbit!")
  }
}

var killerRabbit = Object.create(protoRabbit)
killerRabbit.speak() // -> I am a Proto Rabbit!

To create an object without any prototype (not even Object.prototype) you can use the Object.create method. Since our protoLessObject has no prototype all of the properties will be its own properties, so we won’t need the Object.hasOwnProperty kludge.

var protoLessObject = Object.create(null)