Detailed explanation of function overloading in JavaScript

function addMethod(object, name, fn){    var old = object[name];
    object[name] = function()    {        if (fn.length == arguments.length)            return fn.apply(this, arguments);        else if (typeof old == 'function')            return old.apply(this, arguments);
    };
}// 不传参数时，返回所有namefunction find0(){　　    return this.names;
}// 传一个参数时，返回firstName匹配的namefunction find1(firstName){　　    var result = [];　　    for (var i = 0; i < this.names.length; i++)
    {　　　　        if (this.names[i].indexOf(firstName) === 0)
        {　　　　　　
            result.push(this.names[i]);　　　　
        }　　
    }　　    return result;
}// 传两个参数时，返回firstName和lastName都匹配的namefunction find2(firstName, lastName){　    var result = [];　　    for (var i = 0; i < this.names.length; i++)
    {　　　　        if (this.names[i] === (firstName + " " + lastName))
        {　　　　　　
            result.push(this.names[i]);　　　　
        }　　
    }　　    return result;
}function Users(){
    addMethod(Users.prototype, "find", find0);
    addMethod(Users.prototype, "find", find1);
    addMethod(Users.prototype, "find", find2);
}var users = new Users();
users.names = ["John Resig", "John Russell", "Dean Tom"];console.log(users.find()); // 输出[ &#39;John Resig&#39;, &#39;John Russell&#39;, &#39;Dean Tom&#39; ]console.log(users.find("John")); // 输出[ &#39;John Resig&#39;, &#39;John Russell&#39; ]console.log(users.find("John", "Resig")); // 输出[ &#39;John Resig&#39; ]console.log(users.find("John", "E", "Resig")); // 输出undefined