Fluent Interface in exports of Node.js

標題：Node.js的exports使用流暢介面寫法
Node.js (main.js)：

var my = require('./count.js');
var foo = new my.foo(10, 2);
foo.plus().say();
foo.times().say();

exports js (count.js)：

var foo = function(m, n) {
    this.m = m;
    this.n = n;
    this.answer = 0;
    this.method = "";
};

foo.prototype.plus = function() {
    this.answer = this.m + this.n;
    this.method = "+";
    return this;
};

foo.prototype.times = function() {
    this.answer = this.m * this.n;
    this.method = "*";
    return this;
};

foo.prototype.say = function() {
    console.log("%d %s %d = %d", this.m, this.method, this.n, this.answer);
    return this;
};

exports.foo = foo;

範例結果：
10 + 2 = 12 10 * 2 = 20

說明：
在Node.js中採用流暢介面寫法，並使用exports建立一個外部js，在主程式中require後使用。