💠[[HomeObject]]

🚧 under construction

JS ⟩ types ⟩ object ⟩ method ⟩ HomeObject

🚧

🗺️ 圖表

💈範例

• replit

 const { log } = console;

let animal = {
    sayHi() { log(`I'm a 🐶`) }    // [[HomeObject]] === animal
};

let rabbit = {
    __proto__: animal,
    sayHi() { super.sayHi() }      // [[HomeObject]] === rabbit
};

let plant = {
    sayHi() { log("I'm a ☘️") }    // [[HomeObject]] === plant
};

let tree = {
    __proto__: plant,

    // (non-method syntax for objects❗)
    // ----------------------------------------------------------------
    // ⭐ `rabbit.sayHi` method remembers its [[HomeObject]]❗
    // ⭐ `tree.sayHi` is NOT a method❗
    //    (just a "reference" to another method)
    sayHi: rabbit.sayHi            // [[HomeObject]] === rabbit
    // ----------------------------------------------------------------
};

tree.sayHi();
// super.sayHi()                   // ⭐ in `rabbit.sayHi` method
//
//     super === [[HomeObject]].[[Prototype]]
//           === rabbit.[[Prototype]]
//           === animal
//
// animal.sayHi()                  // "I'm a 🐶"

⭐️ 重點

⭐️ 非常重要：

• only methods have [[HomeObject]].

• [[HomeObject]] can’t be changed.

• super can only be used within methods.

• super === [[HomeObject]].[[Prototype]]⭐️

• a method's HomeObject is only used when calling super.

• if a method does not use super, then we can still consider it "free" (like a free function)

for objects, methods must be specified：

• as method()(method syntax)

• not as nonMethod: function() (non-method syntax)

const { log } = console;

// -------------------------------------------------------------
// ⭐️ only methods have [[HomeObject]].
// ⭐️ `super` can only be used in a method (with [[HomeObject]])
// ⭐️ super === [[HomeObject]].[[Prototype]]
// -------------------------------------------------------------

// ❌ regular function
// --------------------
function f1(){ super.method() }
//             ^^^^^                // ⛔️ SyntaxError: 'super' unexpected here.

// ❌ arrow function (not in a method)
// ------------------------------------
let f2 = () => super.method();
//             ^^^^^                // ⛔️ SyntaxError: 'super' unexpected here.

const a = {
    // ❌ object property (function as property value)
    // ------------------------------------------------
    nonMethod: function(){ super.method() }
    //                     ^^^^^    // ⛔️ SyntaxError: 'super' unexpected here.
}

const b = {
    // ✅ object method:
    // ------------------
    // • [[HomeObject]] === b
    // • super === [[HomeObject]].[[Prototype]]
    //         === b.[[Prototype]]
    //         === Object.prototype
    method(){ log(`${super.constructor.name}`) }
}

b.method();    // Object

📗 參考

• JS.info ⟩

  • [[HomeObject]] - every method remembers its HomeObject.

  • Mixins

👥 相關

• a method's HomeObject is only used when calling super.

• super === [[HomeObject]].[[Prototype]]⭐️

• mixin inheritance is possible through [[HomeObject]].