// author wangbinandi@gmail.com

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;