javascript 观察者模式实现自动刷新

// author [e-mail]

const observable = obj => {
    const observers = Symbol();
    const set = function(target, key, value) {
        const result = Reflect.set(target, key, value);
        //console.log("set key:" + key);
        if ( target[observers].has(key) ) {
            target[observers].get(key).forEach(observer => observer());
        }

        return result;
    }

    const get = function(target, key) {
        const result = Reflect.get(target, key);
        //console.log("get key:" + key);
        if (arguments.callee.caller) {
            if (!target[observers].has(key)) {
                target[observers].set(key, new Set())
            }
            target[observers].get(key).add(arguments.callee.caller);
        }

        return result;
    }

    obj[observers] = new Map(); // string => Set()
    return new Proxy(obj, {set, get});
};

const autorun = fn => fn();

var person = observable({
    firstName: 'Matt',
    lastName: 'Ruby',
    age: 18,
    weight: 50
});

autorun(function () {
    console.log('autorun.getAge: ' + person.firstName + ' ' + person.age);
});

autorun(function () {
    console.log('autorun.getName: ' + person.firstName + ' ' + person.lastName);
});

person.age = 19;
person.weight = 55;
person.firstName = 'test';
person.lastName  = 'MyLast';
console.log(person.lastName);
person.age = 20;