您应该如何设计具有多功能构造函数的库？

Question

Recently I was playing around with writing a small library for music theory in JS. One of the features I wanted to add was a jQuery style selector for creating/finding notes. For example:

Notes("a#") === Note {_note: 0, accidental: 1}

However, the structure of the library looked something akin to:

var Notes = function(sel) {

   // initialisation stuff
   var Note = function() {
        // stuff for note objects
   };

   var scales = {
       ...
   };

   var selector(sel) {
        // evaluate sel
        return new Note(...);
   };

   if(sel !== undefined) {
       return selector(sel);
   }

   return {
       Note: Note,
       scales: scales
   };
};
module.exports = new Notes();

This way, I could use the library like this:

var Notes = require("Notes");
Notes.scales.major.c === [0,2,4,...];

But not like this:

var thisNote = Notes("A#");

As Notes was obviously an object that had been returned from the original Notes function. To use the selector function I'd have to expose it and then call it like this:

var thisNote = Notes.selector("A#");

But I want to mimic the jQuery/sizzle style (I had a bit of a search of jQuery's source, but couldn't find anything that helped).

How can I/should I have approached the design to allow for this kind of functionality? Would using prototypes instead of Closures been a more sensical approach? Or should I have aliased the library's name to another method to achieve the desired effect?

Answer 1

jQuery is like this:

function wrap() {
    // do wrapping of DOM nodes
    return {
        value: function () { /*..*/ },
        add_class: function () { /*..*/ }
    };
}
wrap.extend = function () { /*..*/ }
wrap.ajax = function () { /*..*/ }

wrap("#abc"); // has `.value` and `.add_class)
wrap.ajax();