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What is [[Prototype]]? | |
Every object has a special hidden property called [[Prototype]] which is used to access that object's prototype. | |
prototype object <- [[Prototype]] <- object | |
[[Prototype]] is hidden and internal | |
__proto__ can be used to set [[Prototype]] | |
Fun fact: | |
1. __proto__ is a historical getter/setter for [[Prototype]] | |
2. Object.getPrototypeOf/Object.setPrototypeOf also get/set the prototype | |
3. __proto__ can be either an object or null | |
E.g. | |
let animal = { | |
eats: true | |
}; | |
let rabbit = { | |
jumps: true | |
}; | |
rabbit.__proto__ = animal; | |
// we can find both properties in rabbit now: | |
alert( rabbit.eats ); // true | |
alert( rabbit.jumps ); // true | |
E.g. with new F() | |
let animal = { | |
eats: true | |
}; | |
function Rabbit(name) { | |
this.name = name; | |
} | |
Rabbit.prototype = animal; | |
let rabbit = new Rabbit("White Rabbit"); // rabbit.__proto__ == animal | |
alert( rabbit.eats ); // true | |
Setting Rabbit.prototype = animal | |
literally states the following: "When a new Rabbit is created, assign its [[Prototype]] to animal". | |
const obj = {}; | |
obj.__proto === Object.prototype // true | |
Modern alternatives to __proto | |
const newObj = Object.create(proto[, descriptors]) // where "proto" is the [[Prototype]] of the newObj. Basically similar to const newObj = {}; newObj__proto = proto; | |
const newObj = Object.getPrototypeOf(obj) | |
const newObj = Object.setPrototypeOf(obj, proto) |
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