A rotary knob control for Mootools
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Provides a rotary knob control for Mootools


How to use

This widget aims to provide a rotary knob control for MooTools.

A Knob object can be instantiated with a variety of options, and the library also parses the DOM for elements with class .mooknob, replacing each with an instance of the Knob control.

All knobs require user-supplied styling: details below.

Knobs can be controlled with cursor keys, mouse drags, and double clicks, and provide WIA-ARIA attributes populated from both the initial data, and computed data in real time.

Knobs can monitor and reflect a field with a value attribute.

Controlling the Control

By default, the control increments and decrements by 1. If the control receives keyboard focus, the cursor keys may be used to increment and decrement the value - by 10 if if the shift key is depressed. If the alt/meta key is depressed whilst a cursor key is pressed, the value of the control is set to its maximum or minimum, dependent on the cursor key.

The effect of mouse dragging the control is scaled using the option scale: that is, the number of pixels moved will be multiplied by the value of the scale option (or data-scale attribute) and added to the current value of the knob: the great the range of the knob, the smaller the value of scale. If you do not like the speed of the knob movement in relation to mouse dragging, change scale.


A control can monitor and reflect values of another element's value fileld: such element should be supplied via the monotpr field, as described in 'Options', below.

Initial Control Value

The initial value of the control comes from either the monitor elements' value attribute, or the options.value (which may come from the data-value attribute of the element), or from the element's value attribute, in that order.


As seems to be usual for MooTools, no CSS is supplied. However, the Docs/index.html page contains some examples. A basic gray and round knob can be achieved without graphics if you client supports the border-radius property of CSS3:

.rotary {
	border: 1px solid black;
	background: silver;
	text-align: center;
	border-radius: 50%;
	font-weight: bold;
	width: 32pt;
	height: 32pt;

If select the addpointer option (below), the widget will contain a UTF-8 up-arrow.

WIA-ARIA And Use in HTML, without Javascript

The widget can be configued using the attribute of any element which it consumes. Any option listed under the JavaScript API can be passed as an HTML attribute, prefixed with data-.

The range of values the widget will supports (default ±100) can be set with the aria-valuemin and aria-valuemax attributes of the element, which equate to the object's range option array.

The initial (described above) will be placed in the aria-valuenow and aria-valuetext attributes, as well as in the value attribute, if present, otherwise in the data-value attribute.

For example, the following element will produce a rotary knob with an up-arrow (), an initial value of 5, and range between 0 and 10:

<span id='knob1' 

JavaScript API

The equivalent to the above HTML would be:

new Knob({
	element: 'knob1',
	value: 5,
	range: [0, 10]


The following options are available. Some may be supplied as dataset- attributes when their values are literal.

  • element: the DOM element to replace with this control
  • value: (0) The iInitial value of the control. If not supplied, taken from attributes value or data-value
  • range: ([-100, 100]) The minimum and maximum values. May be supplied in HTML as aria-valuemin and aria-valuemax.
  • scale: (null) Multiplier applied to the number of pixels the mosue may be moved, to acheive change in the value field (see Events, below). This is set automatically upon initialisation, unless the user specifies a value.
  • keychangeby: (1) When arrow keys control the knob, the value field is increased by this factor
  • keychangebywithshift: (10) As keychangeby, above, but for when shift is held.
  • monitor: A name for, or instance of, a DOM element that has a value field that shoudl be monitored for changes, to be reflected by this control. Intended for text input elements.
  • monitorMs: (250) The interval, in milliseconds, at which to check the monitor element, if supplied. The monitor element's value (an aria-related) attribute will also be updated with changes to the control.
  • addpointer: () By default the module (since 0.3) replaces element's content with an up-arrow to the element. Disable this by setting this option to null or false.
  • forceint: (false) Force all values to be integers
  • degreesoffset: (0) Offset, in degrees, to apply to the rotation of the knob. This does not effect the value of the control, only its appearance, and can change the style of the control form a pan control to a volume control, for example. The default is 0 but this may change. completedelay: (500) Number of milliseconds to wait for inactivity before firing the onComplete event.


In addition to the above options, the following events are supported:

  • onMousedown: fired when the knob is clicked
  • onMouseup: fired when the knob is released but before it is rendered
  • onComplete: fired when no changes have taken place for the number milliseconds defined in the completedelay option.
  • onTick: fired as the knob is turned

The options may be passed as HTML dataset attributes by prepending data-. The supplied code is wrapped:

    // Supplied code here

The onTick event is intended to allow the user to adjust the behaviour of the widget, and to allow this widget to affect other objects, using the following object fields:

  • x and y represent the position of the mouse curosr relative to the knob
  • movement contains the greater of these two
  • value contains the calculated value of the knob
  • degrees contains the amount by which the knob will be rotated, after onTick has returned, and can be set in accordance with the value in degrees, as accepted by the CSS3 Transform/rotate property.

Public Methods

  • render: Update the control to reflect the current state of the value field, which may be set by supply a single, numeric argument
  • attach: Called at instantiation to attach eveents to allow the control to operate
  • detach: Removes events


  • Double click support seems to miss the very minimum value of the range.

  • Considering if the knob should support more intuative dragging, dependant upon the knob's current value.


When using HTML mark-up to create a knob, why do *valuemin* and *valuemax* not work?

The acceptable range of inputs should be specified through aria-valuemin and aria-valuemax*, notdata-valueminanddata-valuemax`.

Why are arguments all lower case, rather than camel case?

To make parsing of dataset attributes easier: these are all forced to lower case by the browser.