✨"pure" object

an object without prototype.

JS ⟩ value ⟩ object ⟩ create ⟩ Object.create() ⟩ pure object

Object.create(null) is an object without prototype.

🧨 雷區

this "pure" object will not inherit anything❗

• does not have toString() method.

• won't work with + operator.

• can't call __proto__ (accessor).

💈範例

• replit ⟩ pure object

const { log } = console;

// -----------------------------------
// ⭐ pure object without "prototype"
const obj = Object.create(null);
// -----------------------------------

// ⭐ can't get obj's [[Prototype]] using `__proto__` now.
// ⭐ `__proto__` is a getter/setter that resides in `Object.prototype`.
const proto = Object.getPrototypeOf(obj);    // null

log(obj);        // ⭐ [Object: null prototype]

// to silence the ⛔ TypeError, define `toString`:

// ⭐ regular property is "enumerable"
// obj.toString = () => `hi`;

// ⭐ use `Object.defineProperty` to define a non-enumerable property.
Object.defineProperty(obj, 'toString', {
    value: () => `hi`,
})

// -------------------------------------------------------
// ⛔ TypeError: Cannot convert object to primitive value
// -------------------------------------------------------
log(`${obj}`);    // ⭐ `obj` has no `toString()`❗
// -------------------------------------------------------

;
[
    typeof obj,            // 'object'
    obj instanceof Object, // ⭐ false❗ (你說，JavaScript 是不是很亂搞 🙄)

    Object.keys(obj),      // [ 'toString' ] (if `toString` is enumerable)
                           // [ ]            (if `toString` is non-enumerable)
    
    proto === null,        // true
    obj.__proto__,         // ⭐ undefined❗
    
].forEach(x => log(x));

📗 參考

• JS.info ⟩ "very plain" objects

📘 手冊

• Object.defineProperty()