Rewrite of Chris' implementation of Web MIDI API.

gistfile1.js

(function(exports, global, perf) {
    'use strict';
    var jazzInstances = [];
    if ('getMIDIAccess' in exports) {
        return; // namespace is taken already, bail!
    }
    exports.getMIDIAccess = getMIDIAccess;

    function getMIDIAccess(successCallback, errorCallback) {
        if (typeof successCallback !== 'function') {
            throw new TypeError('expected function');
        }
        new MIDIAccess(successCallback, errorCallback);
    }
    //creates instances of the Jazz plugin (http://jazz-soft.net/)
    function JazzInstance() {
        if (!this instanceof JazzInstance) {
            return new JazzInstance();
        }
        var jazz = loadPlugin(),
            timeZero = 0,
            perfTimeZero = perf.now(),
            interfaces = {
                timeZero: {
                    get: function() {
                        return timeZero;
                    }
                },
                perfTimeZero: {
                    get: function() {
                        return perfTimeZero;
                    }
                },
                time: {
                    get: function() {
                        return jazz.Time();
                    }
                }
            };
        //loads the Jazz plugin by creating an <object>
        function loadPlugin(id, classid) {
            var plugin,
            msg = 'Failed to initialize. Maybe missing Jazz plugin? http://jazz-soft.net/',
                elemId = '_Jazz' + Math.random(),
                objElem = document.createElement('object'),
                fallbackObj = objElem.cloneNode();
            objElem.id = elemId + 'ie';
            objElem.classid = 'CLSID:1ACE1618-1C7D-4561-AEE1-34842AA85E90';
            fallbackObj.id = elemId;
            fallbackObj.type = 'audio/x-jazz';
            objElem.appendChild(fallbackObj);
            document.documentElement.appendChild(objElem);
            plugin = (fallbackObj.isJazz === true) ? fallbackObj : objElem;
            if (!plugin instanceof window.HTMLObjectElement || !(plugin.isJazz)) {
                window.console.error(msg);
                return null;
            }
            return plugin;
        }
        Object.defineProperties(this, interfaces);
        jazzInstances.push(jazz);
    }
    /**
    interface MIDIPort : EventListener {
    readonly attribute DOMString    id;
    readonly attribute DOMString?   manufacturer;
    readonly attribute DOMString?   name;
    readonly attribute MIDIPortType type;
    readonly attribute DOMString?   version;
             attribute EventHandler onmessage;
    }
    */
    function MIDIPort(jazz, type) {
        var dispatcher = document.createElement('x-eventDispatcher'),
            id,
            manufacturer = null,
            version = null,
            interfaces = {
                id: {
                    get: function() {
                        return id;
                    }
                },
                type: {
                    get: function() {
                        return type;
                    }
                },
                version: {
                    get: function() {
                        return version;
                    }
                },

                //EventListener
                addEventListener: {
                    value: function(type, listener, useCapture) {
                        dispatcher.addEventListener(type, listener, useCapture);
                    }
                },
                removeEventListener: {
                    value: function(type, listener, useCapture) {
                        dispatcher.removeEventListener(type, listener, useCapture);
                    }
                },
                dispatchEvent: {
                    value: function(evt) {
                        dispatcher.dispatchEvent(evt);
                    }
                }
            };
            Object.defineProperties(this, interfaces);
    }


    function MIDIAccess(successCallback, errorCallback) {
        var jazz = new JazzInstance(),
            interfaces = {
                enumerateInputs: {
                    value: function() {
                        return enumerateList(this, jazz, 'input');
                    }
                },
                enumerateOutputs: {
                    value: function() {
                        return enumerateList(this, jazz, 'output');
                    }
                },
                getInput: {
                    value: function(target) {
                        return getInput(this, target);
                    }
                },
                getOutput: {
                    value: function(target) {
                        getOutput(this, target);
                    }
                },
                toString: {
                    value: function() {
                        toString.call(this);
                    }
                },
                send: {
                    value: function(data, timestamp) {
                        send(data, timestamp, jazz);
                    }
                }
            };
        Object.defineProperties(this, interfaces);

        function enumerateList(midiAccess, jazz, list, type) {
            for (var items = [], i = 0, l = list.length; i < l; i++) {
                items[i] = new MIDIPort(midiAccess, list[i], i, type);
            }
            return items;
        }

        function getInput(midiAccess, target) {
            return (!! target) ? null : new MIDIInput(midiAccess, target);
        }

        function getOutput(midiAccess, target) {
            return (!! target) ? null : new MIDIOutput(midiAccess, target);
        }

        function toString(midiAccess) {
            var info = 'type: ' + midiAccess.type + "name: '" + midiAccess.name + "' manufacturer: '" + midiAccess.manufacturer + "' version: " + midiAccess.version + " fingerprint: '" + midiAccess.fingerprint + "'";
            return info;
        }

        function mideProc(jazz, timestamp, data) {
            var evt = new global.CustomEvent('message'),
                t = timestamp - jazz._timeZero;
            evt.timestamp = parseFloat(timestamp.toString()) + jazz.perfTimeZero;
            evt.data = new Uint8Array(data);
            dispatcher.dispatchEvent(evt);
        }

        function send(data, timestamp, jazz) {
            var delayBeforeSend = (timestamp) ? Math.floor(timestamp - perf.now()) : 0;
            if (!! (data) || data.length === 0) {
                return false;
            }
            if (timestamp && (delayBeforeSend > 1)) {
                window.setTimeout(send(data, timestamp, jazz), delayBeforeSend);
            } else {
                jazz.MidiOutLong(data);
            }
            return true;
        }
    }
}(window, window.navigator, window.performance));