Components JS is a JavaScript library that makes it easier to code MIDI controller mappings for Mixxx. It lets you focus more on your controller and less on the details of MIDI signals and how Mixxx works. It is centered around JavaScript objects called Components that represent a physical component of a controller, such as a button, knob, fader, or encoder. Components provide generic functions that can be made to work for most use cases just by changing some attributes of the Component, without having to write many or any custom functions. The library also provides more specialized Components for common use cases. Components can be organized into ComponentContainer objects, making it easy to iterate over them and change their behavior to switch between different modes.

Components JS is new in Mixxx 2.1 and does not work with older versions of Mixxx. To use the library, in the <scriptfiles> element at the top of your mapping's XML file, load the Lodash library and the Components library (above the link to your controller's script file):

<file filename="lodash.mixxx.js"/>
<file filename="midi-components-0.0.js"/>
<file functionprefix="MyController" filename="My_Controller_SCRIPT.js"/>

Components JS uses a few functions from Lodash, which is why they both need to be loaded. Importing the midi-components-0.0.js file makes the library accessible by an object called components (plural, lower case).

If you are not familiar with object oriented programming in JavaScript, read Mozilla Developer Network's Object-oriented JavaScript introduction. If you are familiar with OOP in other languages but new to JavaScript, you can skip ahead to the Constructors and object instances section of that tutorial.

To map most controllers, create a custom subtype of #Deck and create instances of your custom Deck objects in your controller's init function. Use the custom Deck's constructor function to create all the Components you need for your particular controller. The example below is for a typical 2 deck controller. If you are mapping a controller with a different layout, some changes to this general structure may be necessary. There is a lot to explain here, so don't worry about understanding every detail just yet:

// Declare the variable for your controller and assign it to an empty object
var MyController = {};

// Mixxx calls this function on startup or when the controller
// is enabled in the Mixxx Preferences
MyController.init = function () {
    // create an instance of your custom Deck object for each side of your controller
    MyController.leftDeck = new MyController.Deck([1, 3], 1);
    MyController.rightDeck = new MyController.Deck([2, 4], 2);
};

MyController.shutdown = function () {
    // send whatever MIDI messages you need to turn off the lights of your controller
};

// implement a constructor for a custom Deck object specific to your controller
MyController.Deck = function (deckNumbers, midiChannel) {
    // Call the generic Deck constructor to setup the currentDeck and deckNumbers properties,
    // using Function.prototype.call to assign the custom Deck being constructed
    // to 'this' in the context of the generic components.Deck constructor
    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call
    components.Deck.call(this, deckNumbers);
    this.playButton = new components.PlayButton([0x90 + midiChannel, 0x01]);
    this.cueButton = new components.CueButton([0x90 + midiChannel, 0x02]);
    this.syncButton = new components.SyncButton([0x90 + midiChannel, 0x03]);
    this.pflButton = new components.Button({
        midi: [0x90 + channel, 0x04],
        key: 'pfl',
    });
    this.hotcueButtons = [];
    for (var i = 1; i <= 8; i++) {
        this.hotcueButtons[i] = new components.HotcueButton({
            midi: [0x90 + midiChannel, 0x10 + i],
            number: i,
        });
    }

    this.volume = new components.Pot({
        midi: [0xB0 + midiChannel, 0x01],
        inKey: 'volume',
    });

    this.eqKnob = [];
    for (var k = 1; k <= 3; k++) {
        this.eqKnob[k] = new components.Pot({
            midi: [0xB0 + midiChannel, 0x02 + k],
            group: '[EqualizerRack1_' + this.currentDeck + '_Effect1]',
            inKey: 'parameter' + k,
        });
    }

    // ... define as many other Components as necessary ...

    // Set the group properties of the above Components and connect their output callback functions
    // Without this, the group property for each Component would have to be specified to its
    // constructor.
    this.reconnectComponents(function (c) {
        if (c.group === undefined) {
            // 'this' inside a function passed to reconnectComponents refers to the ComponentContainer
            // so 'this' refers to the custom Deck object being constructed
            c.group = this.currentDeck;
        }
    });
    // when called with JavaScript's 'new' keyword, a constructor function
    // implicitly returns 'this'
};
// give your custom Deck all the methods of the generic Deck in the Components library
MyController.Deck.prototype = new components.Deck();

The basic building block of the library are Component objects that represent a physical component of a controller, such as a button, knob, fader, or encoder. The JavaScript object encapsulates all the information needed to receive MIDI input from that component and send MIDI signals out to the controller to activate its LED(s).

Components should generally be properties of a ComponentContainer object. Most Components should be properties of a custom #Deck object as demonstrated in the example in the previous section.

In general, you should not use the basic Component constructor directly; instead, use one of its subtypes (Button, Pot, or Encoder). If you do need to use Component directly, do not confuse it with the components object (plural, lower case) that contains all the objects for the library; access Component as components.Component (plural lower case then singular upper case).

The input function of each Component needs to be mapped to the incoming MIDI signals in the XML file. For example:

<control>
    <group>[Channel1]</group>
    <!-- MyController.leftDeck would be an instance of a custom Deck. -->
    <key>MyController.leftDeck.quantizeButton.input</key>
    <status>0x90</status>
    <midino>0x01</midino>
    <options>
        <script-binding/>
    </options>
</control>

In the future Mixxx will be able to register MIDI inputs from JavaScript, so that will not be necessary. Until then, if you decide to rename a Component or map it to different MIDI input signals, you need to edit the XML file and reload the mapping in Mixxx's Preferences. The output does not need to be mapped in XML. It is handled by the library in JavaScript.

Create Components by calling the constructor with JavaScript's new keyword. The Component constructor takes a single object as an argument. Generally you should provide this as an object literal. Each property of that object passed to the constructor becomes a property of the new Component object, making it easy to customize the functionality of the Component. The constructors for all Component subtypes work the same way. Most Components need at least these properties defined:

• midi (array with 2 numbers): the first two MIDI bytes that the controller sends/receives when the physical component changes state. Refer to the MIDI Crash Course if you do not understand what this means.
• inKey (string): the key of the Mixxx ControlObject that this Component manipulates when it receives a MIDI input signal
• outKey (string): when the Mixxx ControlObject specified by this key changes value, the output function will be called
• group (string): the group of the Mixxx ControlObjects for both inKey and outKey, for example [Channel1] for deck 1

For example:

var quantizeButton = new components.Button({
    midi: [0x91, 0x01],
    group: '[Channel1]'
    inKey: 'quantize',
    outKey: 'quantize',
});

If inKey and outKey are the same, you can specify key in the options object for the constructor to set both the inKey and outKey properties of the new Component. For example:

var quantizeButton = new components.Button({
    midi: [0x91, 0x01],
    group: '[Channel1]',
    key: 'quantize',
});

Setting the key property after calling the constructor will not automatically set inKey and outKey; you would need to do that manually if necessary.

The following methods (in JavaScript, methods are just object properties that happen to be functions) must be defined for every Component, but in most cases the defaults (from the inherited prototype Component) will work so you do not need to define them yourself:

• input: the function that receives MIDI input
• output: the function that gets called when outKey changes value. Typically this sends MIDI output to the controller to change the state of an LED, but it can do anything.
• connect: register output as the callback function that gets executed when the value of the Mixxx ControlObject specified by group, outKey changes. This is called automatically by the Component constructor if group and outKey are defined (otherwise it needs to be called after construction). Implement a custom function if you need to connect callbacks for multiple Mixxx ControlObjects in one Component. Refer to the source code of SamplerButton.prototype.connect for an example.

The following methods are called by the default Component input and output methods, as well as the default input functions of Button, Pot, and Encoder. If you do not need to implement complex custom behavior, you can overwrite these instead of the default input and output methods:

• inValueScale: takes the third byte of the incoming MIDI signal as its first argument and returns the value to set group, inKey to
• outValueScale: takes the value of group, outKey as its first argument and returns the third byte of the outgoing MIDI signal

Each Component also has these methods that you probably should not overwrite:

• disconnect: disconnect the output function from being called when group, outKey changes
• trigger: manually call output with the same arguments as if group, outKey had changed
• send: send a 3 byte (short) MIDI message out to the controller. The first two bytes of the MIDI message are specified by the Component's midi property. The third MIDI byte is provided as the first argument to the send function.
• inGetParameter: returns the value of group, inKey normalized to a 0-1 scale
• inSetParameter: sets the value of group, inKey to the function's first argument, normalized to a 0-1 scale
• inGetValue: returns the value of group, inKey
• inSetValue: sets the value of group, inKey to the function's first argument
• inToggle: sets group, inKey to its inverse (0 if it is >0; 1 if it is 0)
• outGetParameter: returns the value of group, outKey normalized to a 0-1 scale
• outSetParameter: sets the value of group, outKey to the function's first argument, normalized to a 0-1 scale
• outGetValue: returns the value of group, outKey
• outSetValue: sets the value of group, outKey to the function's first argument
• outToggle: sets group, outKey to its inverse (0 if it is >0; 1 if it is 0)

The following properties can be specified in the options object passed to the Component constructor to customize the Component's initialization. Changing their value after creating the Component does not do anything.

• outConnect (boolean, default true): whether to call connect in the constructor (assuming group and outKey were specified in the options object)
• outTrigger (boolean, default true): whether to call trigger in the constructor (assuming group and outKey were specified in the options object)

Some controllers send and receive two sets of MIDI signals for most physical components, one for when the shift button is pressed and one for when the shift button is not pressed. To avoid defining two Components for every physical component of your controller, set the following options as appropriate:

• sendShifted (boolean, default false): whether to send a second, shifted MIDI message for every call to send
• shiftChannel (boolean, default false): whether the shifted MIDI message changes the MIDI channel (second nybble of the first byte of the MIDI signal)
• shiftControl (boolean, default false): whether the shifted MIDI message changes the MIDI control number (second byte) of the MIDI signal
• shiftOffset (number, default 0): how much to shift the MIDI channel or control number by

To avoid having to define those properties for every Component, you can change the properties of components.Component.prototype in your controller's init function. For example:

components.Component.prototype.shiftOffset = 3;
components.Component.prototype.shiftChannel = true;
components.Component.prototype.sendShifted = true;

Components JS provides convenient shortcuts for common situations.

To avoid typing out the group for the constructor of each Component, Components that share a group can be part of a ComponentContainer and the ComponentContainer's reconnectComponents method can assign the group to all of them. Refer to the #Deck ComponentContainer documentation for an example.

If a Component only needs its midi property specified for its constructor, this can be provided simply as an array without wrapping it in an object. For example:

var playButton = new components.PlayButton([0x90 + channel, 0x0A]);

instead of

var playButton = new components.PlayButton({
    midi: [0x90 + channel, 0x0A]
});

A Button is a subtype of Component for buttons/pads. Subtypes of Button are provided for many common use cases, documented in the subsections below, making it easy to map those buttons without having to worry about particularities of Mixxx's ControlObjects. To use the Button subtypes, you only need to specify their midi and group properties, except for HotcueButton and SamplerButton.

A generic Button toggles the state of a binary inKey and sends outgoing MIDI messages indicating whether a binary outKey is on or off. Button adds the following properties to Component:

• type: determines the behavior of the Button. Can be any of these values:
  • Button.prototype.types.push (default): set inKey to 1 on button press and 0 on button release. For example, use this type with the beatloop_activate Control
  • Button.prototype.types.toggle: invert value of inKey on button press. Use this with Controls whose values indicate the state of a switch, for example pfl
  • Button.prototype.types.powerWindow: like toggle, but toggles the value of inKey again on button up when long pressed, for example with [EffectRack1_EffectUnit2_Effect1], enabled Control.
• on (number, default 127): number to send as the third byte of outgoing MIDI messages when group, outKey is on (its value is > 0)
• off (number, default 0): number to send as the third byte of outgoing MIDI messages when group, outKey is off (its value is 0)
• isPress (function): function that takes the same first 4 arguments as a MIDI input function (channel, control, value, status) and returns a boolean indicating whether the button was pressed.

For buttons/pads with multicolor LEDs, you can change the color of the LED by defining the on and off properties to be the MIDI value to send for that state. For example, if the LED turns red when sent a MIDI value of 127 and blue when sent a value of 126:

MyController.padColors = {
    red: 127,
    blue: 126
};
MyController.quantize = new components.Button({
    midi: [0x91, 0x01],
    group: '[Channel1]',
    key: 'quantize',
    type: components.Button.prototype.types.toggle,
    on: MyController.padColors.red,
    off: MyController.padColors.blue,
});

The default isPress function works for controllers that indicate whether a button is pressed or released by sending a different third MIDI byte (value). Some controllers distinguish between a button press and release by changing the first nybble (hexadecimal digit) of the first byte of the MIDI message, also known as an opcode. These controllers typically use an opcode of 9 to indicate a button press and 8 to indicate a button release. Both the press and release signals need to be mapped in the XML file to the Button's input method. To make Button work for such a controller, reimplement the prototype isPress function:

components.Button.prototype.isPress = function(channel, control, value, status) {
    return (status & 0xF0) === 0x90;
}

Default behavior: play/pause Shift behavior: reverse playback

LED behavior depends on cue mode selected by the user in the preferences Refer to the manual for details.

Default behavior: depends on cue mode configured by the user in the preferences Shift behavior: stop playback and go to start of track Refer to the manual for details.

Default behavior: momentary sync without toggling sync lock Shift behavior: toggle sync lock (master sync)

Default behavior: set hotcue if it is not set. If it is set, jump to it. Shift behavior: delete hotcue

The LED indicates whether the hotcue is set.

Pass the number of the hotcue as the number property of the options argument for the constructor. For example:

var hotcues = [];
for (var i = 1; i <= 8; i++) {
    hotcues[i] = new components.HotcueButton({
        number: i,
        group: '[Channel1]',
        midi: [0x91, 0x26 + i],
    });
}

HotcueButton can show hotcue colors on the controller. There are three ways of implementing this. Which one to choose depends on the controller.

1. Set color via single byte based on controller internal palette
2. Set color via SysEx based on custom palette.
3. Set color via SysEx based on predefined colors by Mixxx.

Option 1 is the simplest and most common method for most controllers. You must figure out which MIDI values correspond to which colors and the correlate it with the predefined hotcue colors (the controller's manual from the manufacturer may document this). Creating such HotcueButton could look like this:

var hotcueButton = new components.HotcueButton({
    number: 1,
    group: '[Channel1]',
    midi: [0x91, 0x26],
    // key-value map to correlate the Mixxx ColorID
    // with the value the controller expects for
    // specific colors. These values are passed to
    // the HotcueButton's send method.
    colors: {
        0: 0x10,
        1: 0x18,
        2: 0x20,
        ...
    },
    // value to turn off the buttons LED.
    off: 0x00,
});

With the second option, you can send predefined colors from the palette to the controller but this time via SysEx. Since SysEx is very controller specific, it is mandatory to specify a custom sendRGB method which is responsible for taking a color description, extracting the relevant information, and sending the SysEx Message to the controller. In this case, the values of the attributes in the colors object are passed as the input to the sendRGB method.

var hotcueButton = new components.HotcueButton({
    number: 1,
    group: '[Channel1]',
    midi: [0x91, 0x26],
    // key-value map to correlate the Mixxx ColorID
    // with an array which contains (in this case)
    // the RGB components of a color. These values
    // are passed as input to the sendRGB method.
    colors: {
        0: [0x00,0x00,0x00], // black
        1: [0xFF,0x00,0x00], // pure red
        2: [0xFF,0xFF,0x00], // pure Yellow
        ...
    },
    sendRGB: function (color_obj) {
        // example Message (hardcoded bytes are controller specific).
    // colors entries contain 8-bit values, but SysEx only supports 7-bit values
    // so were bitshifting by 1 to reduce the resolution.
        var msg = [0xF0, 0x00, 0x01, color_obj[0]>>1,color_obj[1]>>1,color_obj[2]>>1];
        // send message
    midi.sendSysexMsg(msg, msg.length);
    }
});

The third option is similar to the second one. You need to define a sendRGB method again, but in this Mixxx provides the color palette automatically and you do not provide a colors object for the HotcueButton. The sendRGB(color) method gets passed a color object (more on the color API here). Such a button could be defined like this:

var hotcueButton = new components.HotcueButton({
    number: 1,
    group: '[Channel1]',
    midi: [0x91, 0x26],
    // colors automatically assigned by Components.JS framework
    sendRGB: function (color_obj) {
        // example Message (hardcoded bytes are controller specific).
    // colors entries contain 8-bit values, but SysEx only supports 7-bit values
    // so were bitshifting by 1 to reduce the resolution.
        var msg = [0xF0, 0x00, 0x01, color_obj.red>>1,color_obj.green>>1,color_obj.blue>>1];
        // send message
    midi.sendSysexMsg(msg, msg.length);
    }
});

Default behavior: Press the button to load the track selected in the library into an empty sampler. Press a loaded sampler to play it from its cue point. Press again while playing to jump back to the cue point. Shift behavior: If the sampler is playing, stop it. If the sampler is stopped, eject it.

Specify the sampler number as the number property of the object passed to the constructor. There is no need to manually specify the group. For example:

var samplerButtons = [];
for (var n = 1; n <= 8; n++) {
    samplerButtons[n] = new components.SamplerButton({
        number: n,
        midi: [0x91, 0x02],
    });
};

You can also make the SamplerButtons velocity sensitive by setting the volumeByVelocity: true property on the object that gets passed to the constructor. This will change the volume at which the sample is being played at depending on how hard you pressed the button. Obviously, it will only work if your hardware features velocity sensitive buttons.

var samplerButtons = [];
for (var n = 1; n <= 8; n++) {
    samplerButtons[n] = new components.SamplerButton({
        number: n,
        midi: [0x91, 0x02],
        volumeByVelocity: true,
    });
};

When the sampler is loaded, the LED will be sent a MIDI message with the value of the on property (default 127) When the sampler is empty, the LED will be sent a MIDI message with the value of the off property (default 0). If your controller's pads have multicolor LEDs, specify the value to send for a different LED color with the playing property to set the LED to a different color while the sampler is playing. For example:

MyController.padColors = {
// These values are just examples, consult the MIDI documentation from your controller's
// manufacturer to find the values for your controller. If that information is not available,
// guess and check to find the values.
    red: 125,
    blue: 126,
    purple: 127,
    off: 0
};
var samplerButton = [];
var samplerButton[1] = new components.SamplerButton({
    midi: [0x91, 0x02],
    number: 1,
    on: MyController.padColors.blue,
    playing: MyController.padColors.red,
    // off is inherited from Button.prototype
});

An EffectAssignmentButton routes a deck through an EffectUnit. It is separate from the EffectUnit ComponentContainer because it is-meant to be a part of a Deck. Using Deck.setCurrentDeck to switch decks will switch the deck an EffectAssignmentButton assigns an EffectUnit to.

var effectAssignmentButtons = [];
for (var u = 1; u <= 4; u++) {
    effectAssignmentButtons = new components.EffectAssignmentButton({
        midi: [0x92, 0x20 + u],
        effectUnit: u,
        group: '[Channel1]',
    });
}

A Pot is a Component subtype for potentiometers (faders and knobs) with finite ranges. Pot's connect and disconnect methods take care of soft takeover when switching layers with ComponentContainer's reconnectComponents or applyLayer methods. Soft takeover is not activated until the first input signal is received, so it does not interfere with setting initial values for controllers that can report that information.

For example:

var eqKnobs = [];
for (var i = 1; i <= 3; i++) {
    eqKnobs[i] = new components.Pot({
        midi: [0xB1, 0x02 + i],
        group: '[EqualizerRack1_[Channel1]_Effect1]',
        inKey: 'parameter' + i,
    });
}

To use a Pot with a fader or knob that uses 14 bit MIDI (sends two MIDI messages, one with a least significant byte and one with a most significant byte) for higher precision, map the incoming signals to the Pot's inputLSB and inputMSB functions instead of input in the XML file. Nothing extra needs to be done in JavaScript.

The Pot components supports max values up to 16384 (2^14). So if (for some obscure reason) a control only sends 6 bytes of precision, you can map input as if the control had 7 bits of precision and then specify max: 64. The same would work for 10 bits for example, just map inputLSB and inputMSB as if the control sent 14 bits of precision and then specify max: 1024.

By default the Pot Component will try to deal with soft-takeover for you, but if that interferes with your component or is unnecessary (for example when the Component never switches layers), you can specify softTakeover: false to disable it.

Pot Components support an optional relative mode as an alternative to dealing with soft takeover. To use it, set the relative property to true in the options object for the constructor. In this mode, moving the Pot will adjust the Mixxx Control relative to its current value. For example:

var tempoFader = new components.Pot({
    midi: [0xB1, 0x32],
    group: '[Channel1]',
    inKey: 'rate',
    relative: true,
});

Encoder is a Component for infinitely turning encoders. The default input function assumes the encoder sends MIDI signals on a continous scale from 0 to 127 (0x7F). If the encoder sends relative MIDI signals to indicate whether it turns right or left, you will need to define your own input function. For example, for an encoder that sends a value of 1 when it is turned left and a value of 127 when it is turned right:

MyController.SomeEncoder = new components.Encoder({
    midi: [0xB1, 0x03],
    group: '[Channel1]',
    inKey: 'pregain',
    input: function (channel, control, value, status, group) {
        if (value === 1) {
            this.inSetParameter(this.inGetParameter() - .05);
        } else if (value === 127) {
            this.inSetParameter(this.inGetParameter() + .05);
        }
    },
});

To map an Encoder with an LED ring around it that receives MIDI signals on a continuous 0-127 scale, define an outKey property in the options object for the constructor. Similar to input, if the LEDs do not respond to a continuous 0-127 scale, define your own output function. If outKey and inKey are the same, you can just specify one key property for the constructor.

Encoders can often be pushed like a button. Usually, it is best to use a separate Button Component to handle the MIDI signals from pushing it.

Since mapping Jogwheels in mixxx can be cumbersome we introduced a new component called JogWheelBasic in Mixxx 2.3.4.

this.jogWheel = components.JogWheelBasic({
  deck: 1, // whatever deck this jogwheel controls
  wheelResolution: 1000, // how many ticks per revolution the jogwheel has
  alpha: 1/8 // alpha-filter
  beta: 1/8/32 // optional
  rpm: 33 + 1/3 // optional
  group: // optional
});

See the Jogwheel guide on a more in-depth explanation of the available properties. The XML should map jogWheel.inputWheel to the messages containing rotation information of the wheel and jogWheel.inputTouch on messages that contain info on whether the top of the platter was touched. If you need to make some adjustments how the wheel interprets the incoming rotation information, you can overwrite onValueScale(midiValue). If your controller has an option to enable/disable vinylmode, you can set jogWheel.vinylMode and the controller will behave appropriately (touching the jogwheel platter is ignored when vinylMode is false).

A ComponentContainer is an object that contains Components as properties. ComponentContainer has methods to easily iterate through the Components, which makes it easy to manage different layers of functionality. The basic ComponentContainer methods are:

• forEachComponent: Iterate over all Components in this ComponentContainer and perform an operation on them. The operation is a function provided as the first argument to forEachComponent. The operation function takes each Component as its first argument. In the context of the operation function, this refers to the ComponentContainer. forEachComponent iterates recursively through the Components in any ComponentContainers and arrays that are properties of this ComponentContainer. If you do not want forEachComponent to operate recursively, pass false as the second argument to forEachComponent.
• reconnectComponents: Call each Component's disconnect method, optionally perform an operation on it, then call its connect and trigger methods to sync the state of the controller's LEDs. Arguments are the same as forEachComponent.
• shutdown: Iterate over all Components and call their shutdown methods. The Button is the only component with a predefined shutdown method. All other components have to be implemented manually if they require anything to be done when Mixxx shuts down.

Typically, reconnectComponents is used to switch between layers. The callback passed to reconnectComponents can manipulate each Component's properties as appropriate for the new layer. Below is a basic example for switching between decks 1 and 3. This is a simple example that does not handle the complexities presented by EQs, QuickEffects, or EffectAssignmentButtons like Deck.setCurrentDeck does.

// Define a constructor for a ComponentContainer that adds some Components to it
var ExampleContainer = function () {
    this.play = new components.PlayButton({
        midi: [0x91, 0x40],
        group: '[Channel1]',
    });
    this.cue = new components.CueButton({
        midi: [0x91, 0x41],
        group: '[Channel1]',
    });
};
// This will give any object created with "new exampleContainer()"
// the ComponentContainer methods.
exampleContainer.prototype = new components.ComponentContainer();

var demonstration = new ExampleContainer();
demonstration.reconnectComponents(function (component) {
    component.group = '[Channel3]';
)};

In simple cases like the demonstration above, changing a property of each Component in the callback passed to reconnectComponents is sufficient. When more complex manipulation is required, especially if the manipulation varies between Components, it is a good idea to use the reconnectComponents callback to call a specific method on each Component. This keeps all the logic for that Component together instead of scattering it between the Component construction and the layer switching function.

The most common use case for changing layers is for shift buttons. If your controller sends different MIDI signals depending on whether shift is pressed, map both the shifted and unshifted input signals to the Component's input function in XML. For each Component that has different behavior depending on whether shift is pressed, implement shift and unshift methods that manipulate the Component appropriately. When the shift button is pressed call ComponentContainer.shift() and the shift method of each Component in the ComponentContainer will be executed (if it exists). When the shift button is released, call ComponentContainer.unshift() to call each Component's unshift method.

Note that any Button.prototype.types.push type Buttons in the ComponentContainer will have their inKey reset to 0 if the user happens to have them pressed when ComponentContainer.shift() or ComponentContainer.unshift() is called. This prevents the Button's inKey from getting stuck in a pressed (1) state, which can cause confusing behavior with some MixxxControls.

For convenience, the Component constructor will automatically call the unshift function if it exists. This allows you to avoid redundancy when constructing Components.

To use separate output callback functions in shifted and unshifted modes, the Component's shift and unshift functions need to call disconnect/connect and trigger. ComponentContainer's shift/unshift methods will not do this automatically like reconnectComponents.

Generally, you should avoid making LEDs change when a shift button is pressed. This is distracting if the user is pressing shift to use the shifted functionality of a different part of the controller. If the alternate layer is confined to a specific part of the controller, changing LEDs is not an issue.

To handle the interaction of shifted and unshifted states with another layer, you can create another system of methods for each Component that changes properties of the Component when a layer is activated, and within those methods, you can assign the shift and unshift properties of the Component to different functions. Refer to the source code of #EffectUnit for an example.

Deck is a #ComponentContainer with methods for conveniently changing the group attributes of contained Components to switch the deck that a set of Components is manipulating. The setCurrentDeck method takes the new deck as a string and sets the Components' group property appropriately, including for equalizer knobs and QuickEffect (filter) knobs.

The Deck constructor takes one argument, which is an array of deck numbers to cycle through with the toggle method. Typically this will be [1, 3] or [2, 4].

Refer to the #File structure section above for an example.

EffectUnit is a #ComponentContainer that contains Components designed to be mapped to the common arrangement of 4 knobs and 4 buttons for controlling effects. If your controller's effects section has fewer components, the EffectUnit object provided by Components JS probably will not be very helpful. You may want to read the source code for the library's EffectUnit to get an idea for how to map your controller though.

There is no need to use Components for the rest of your mapping if you just want to use the EffectUnit from the library.

The Components provided are:

• dryWetKnob (#Pot)
• effectFocusButton (#Button)
• enableButtons[1-3] (#ComponentContainer of #Buttons)
• knobs[1-3] (#ComponentContainer of #Pots)

Refer to the Standard Effects Mapping page for a description of how to use the EffectUnit object. On the wiki page for your controller, link to the Standard Effects Mapping page instead of rewriting a description for your controller.

To map an EffectUnit for your controller, call the constructor like the #Deck constructor. The only argument to the constructor is an array of numbers that specifies which EffectUnits pressing the effectFocusButton with shift toggles between. Then, set the midi attributes for the showParametersButton, enableButtons[1-3], and optionally enableOnChannelButtons. After the midi attributes are set up, call the EffectUnit's init method to set up the output callbacks. For example:

MyController.effectUnit = new components.EffectUnit([1, 3]);
MyController.effectUnit.enableButtons[1].midi = [0x90, 0x01];
MyController.effectUnit.enableButtons[2].midi = [0x90, 0x02];
MyController.effectUnit.enableButtons[3].midi = [0x90, 0x03];
MyController.effectUnit.knobs[1].midi = [0xB0, 0x01];
MyController.effectUnit.knobs[2].midi = [0xB0, 0x02];
MyController.effectUnit.knobs[3].midi = [0xB0, 0x03];
MyController.effectUnit.dryWetKnob.midi = [0xB0, 0x04];
MyController.effectUnit.effectFocusButton.midi = [0x90, 0x04];
MyController.effectUnit.init();

Controllers designed for Serato and Rekordbox often have an encoder instead of a dry/wet knob (labeled "Beats" for Serato or "Release FX" for Rekordbox) and a button labeled "Tap". Map the effectFocusButton to the controller's "Tap" button. To use the dryWetKnob Pot with an encoder, replace its input function with a function that can appropriately handle the signals sent by your controller. For example:

MyController.effectUnit = new components.EffectUnit([1, 3]);
MyController.effectUnit.enableButtons[1].midi = [0x90, 0x01];
MyController.effectUnit.enableButtons[2].midi = [0x90, 0x02];
MyController.effectUnit.enableButtons[3].midi = [0x90, 0x03];
MyController.effectUnit.knobs[1].midi = [0xB0, 0x01];
MyController.effectUnit.knobs[2].midi = [0xB0, 0x02];
MyController.effectUnit.knobs[3].midi = [0xB0, 0x03];
MyController.effectUnit.dryWetKnob.midi = [0xB0, 0x04];
MyController.effectUnit.dryWetKnob.input = function (channel, control, value, status, group) {
    if (value === 1) {
       // 0.05 is an example. Adjust that value to whatever works well for your controller.
       this.inSetParameter(this.inGetParameter() - .05);
    } else if (value === 127) {
       this.inSetParameter(this.inGetParameter() + .05);
    }
};
MyController.effectUnit.effectFocusButton.midi = [0x90, 0x04];
MyController.effectUnit.init();

For the shift functionality to work, the shift button of your controller must be mapped to a function that calls the shift/unshift methods of the EffectUnit on button press/release. Also, if your controller sends different MIDI signals when shift is pressed, map those as well as the unshifted signals to the input method of each Component in your XML file. If the EffectUnit is a property of another #ComponentContainer (for example a #Deck), calling shift and unshift on the parent ComponentContainer will recursively call it on the EffectUnit too (just like it will for any other ComponentContainer).

By default an effect can only be focused when the respective GUI unit is expanded: when the focus button of a collapsed unit is pressed, the GUI counterpart is expanded. Accordingly, units release the effect focus and switch back to Meta knob mapping as soon as an unit is collapsed. However, there are situations when the on-screen parameters of a focused effect can safely stay hidden while the controller is mapped to the parameter knobs. Collapsed units show a focus indicator then. To enable this mode instatiate effect units with 'true' added after the effect unit numbers array. For example:

MyController.effectUnit = new components.EffectUnit([1, 3],true);
//...

Generally, most controllers should use EffectAssignmentButtons in Decks to enable effect units on decks. If you have a dedicated effects controller that does not manipulate decks, the enableOnChannelButtons provided by EffectUnit would be more appropriate. You can easily create these by calling enableOnChannelButtons.addButton('CHANNEL_NAME') (do not put brackets around the CHANNEL_NAME) on the EffectUnit object, then define their midi properties.