Async JavaScript loader & dependency manager

/*!
 * $script.js JS loader & dependency manager
 * https://github.com/ded/script.js
 * (c) Dustin Diaz 2014 | License MIT
 */

(function(name, definition) {
    if (typeof module != "undefined" && module.exports)
        module.exports = definition();
    else if (typeof define == "function" && define.amd) define(definition);
    else this[name] = definition();
})("$script", function() {
    var doc = document,
        head = doc.getElementsByTagName("head")[0],
        s = "string",
        f = false,
        push = "push",
        readyState = "readyState",
        onreadystatechange = "onreadystatechange",
        list = {},
        ids = {},
        delay = {},
        scripts = {},
        scriptpath,
        urlArgs;

    function every(ar, fn) {
        for (var i = 0, j = ar.length; i < j; ++i) if (!fn(ar[i])) return f;
        return 1;
    }
    function each(ar, fn) {
        every(ar, function(el) {
            fn(el);
            return 1;
        });
    }

    function $script(paths, idOrDone, optDone) {
        paths = paths[push] ? paths : [paths];

        var idOrDoneIsDone = idOrDone && idOrDone.call,
            done = idOrDoneIsDone ? idOrDone : optDone,
            id = idOrDoneIsDone ? paths.join("") : idOrDone,
            queue = paths.length;

        function loopFn(item) {
            return item.call ? item() : list[item];
        }

        function callback() {
            if (!--queue) {
                list[id] = 1;
                done && done();
                for (var dset in delay) {
                    every(dset.split("|"), loopFn) &&
                        !each(delay[dset], loopFn) &&
                        (delay[dset] = []);
                }
            }
        }

        setTimeout(function() {
            each(paths, function loading(path, force) {
                if (path === null) return callback();
                if (!force && !/^https?:\/\//.test(path) && scriptpath) {
                    path =
                        path.indexOf(".js") === -1
                            ? scriptpath + path + ".js"
                            : scriptpath + path;
                }

                if (scripts[path]) {
                    if (id) ids[id] = 1;
                    return scripts[path] == 2
                        ? callback()
                        : setTimeout(function() {
                              loading(path, true);
                          }, 0);
                }

                scripts[path] = 1;
                if (id) ids[id] = 1;

                create(path, callback);
            });
        }, 0);

        return $script;
    }

    function create(path, fn) {
        var el = doc.createElement("script"),
            loaded;

        el.onload = el.onerror = el[onreadystatechange] = function() {
            if ((el[readyState] && !/^c|loade/.test(el[readyState])) || loaded)
                return;
            el.onload = el[onreadystatechange] = null;
            loaded = 1;
            scripts[path] = 2;
            fn();
        };

        el.async = 1;
        el.src = urlArgs
            ? path + (path.indexOf("?") === -1 ? "?" : "&") + urlArgs
            : path;

        head.insertBefore(el, head.lastChild);
    }

    $script.get = create;

    $script.order = function(scripts, id, done) {
        (function callback(s) {
            s = scripts.shift();
            !scripts.length ? $script(s, id, done) : $script(s, callback);
        })();
    };

    $script.path = function(p) {
        scriptpath = p;
    };

    $script.urlArgs = function(str) {
        urlArgs = str;
    };

    $script.ready = function(deps, ready, req) {
        deps = deps[push] ? deps : [deps];
        var missing = [];
        !each(deps, function(dep) {
            list[dep] || missing[push](dep);
        }) &&
        every(deps, function(dep) {
            return list[dep];
        })
            ? ready()
            : !(function(key) {
                  delay[key] = delay[key] || [];
                  delay[key][push](ready);
                  req && req(missing);
              })(deps.join("|"));
        return $script;
    };

    $script.done = function(idOrDone) {
        $script([null], idOrDone);
    };

    return $script;
});