Javascript：将2个对象组合为一个

Question

Is it possible to define a variable C to be a combination of 2 objects(let's say A and B), so that anything happens to A and B at any time in the future will happen to C. This means, C is declared before any change to A and B . For example:

var A = {};
var B = {};
var C = combine(A, B);

A.a=1;
B.b=2;

console.log(C);
// { a:1, b:2 }

Answer 1

C would have to be a function:

function extend(obj) {
    if (typeof obj !== 'object') return obj;
    Array.prototype.slice.call(arguments, 1).forEach(function (source) {
        for (var prop in source) {
            obj[prop] = source[prop];
        }
    });
    return obj;
};

var A = {};
var B = {};
var C = function () {
    var _c = {};
    return extend(_c, A, B);
};

Then call C like:

A.a=1;
B.b=2;

console.log(C());
// { a:1, b:2 }