private implement

private.js

// 存放类的私有字段和对应`Symbol`的映射
let pirvateSymbols = new Map();

let addPrivateSymbol = (klass, key, defualtValue) => {
    let symbol = new Symbol(key);
    let symbols = pirvateSymbols.get(klass) || {};
    symbols[symbol] = defualtValue;
    pirvateSymbols.set(klass, symbols);
};

// 私有方法，用在方法上
let privateMethod = (target, key, descriptor) => {
    addPrivateSymbol(target, key, descriptor.value);

    delete descriptor.value;
    descriptor.enumerable = false;
    descriptor.writable = false;
    descriptor.get = () => throw new ReferenceError();
    return descriptor;
};

// 私有成员
let privateMember = function (name, defaultValue) {
    let symbol = new Symbol(name);

    return target => {
        addPrivateSymbol(target, name, defaultValue);

        target.prototype[symbol] = defaultValue;
    };
}

let privates = (instance) => {
    let klass = instance.constructor;

    return Object.entries(pirvateSymbols.get(klass)).reduce(
        (store, [symbol, key]) => {
            let descriptor = {
                enumerable: false,
                configurable: false
                get() {
                    return this[symbol];
                },
                set(value) {
                    this[symbol] = value;
                }
            };
            Object.defineProperty(store, key, descriptor);
            return store;
        },
        {}
    );
};

@privateMember('alice', 1)
@privateMember('bob')
class Fuck {
    foo() {
        let privates = privates(this);
        privates.bob = (privates.bob || 0) + 1;
        privates.bar.call(this, privates.alice, privates.bob);
    }

    @privateMethod
    bar() {

    }
}

let i = new Fuck();
i.bar(); // ReferenceError
i.alice; // undefined
i.bob; // undefined