# Yahoo! UI Library

### slider 3.1.1

Yahoo! UI Library > slider > clickable-rail.js (source view)
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    /**
     * Adds support for mouse interaction with the Slider rail triggering thumb
     * movement.
     *
     * @module slider
     * @submodule clickable-rail
     */

    /**
     * Slider extension that allows clicking on the Slider's rail element,
     * triggering the thumb to align with the location of the click.
     *
     * @class ClickableRail
     */
    function ClickableRail() {
        this._initClickableRail();
    }

    Y.ClickableRail = Y.mix( ClickableRail, {

        // Prototype methods added to host class
        prototype: {

            /**
             * Initializes the internal state and sets up events.
             *
             * @method _initClickableRail
             * @protected
             */
            _initClickableRail: function () {
                this._evtGuid = this._evtGuid || ( Y.guid() + '|' );

                /**
                 * Broadcasts when the rail has received a mousedown event and
                 * triggers the thumb positioning.  Use
                 * <code>e.preventDefault()</code> or
                 * <code>set(&quot;clickableRail&quot;, false)</code> to prevent
                 * the thumb positioning.
                 *
                 * @event railMouseDown
                 * @preventable _defRailMouseDownFn
                 */
                this.publish( 'railMouseDown', {
                    defaultFn: this._defRailMouseDownFn
                } );

                this.after( 'render', this._bindClickableRail );
                this.on( 'destroy', this._unbindClickableRail );
            },

            /**
             * Attaches DOM event subscribers to support rail interaction.
             *
             * @method _bindClickableRail
             * @protected
             */
            _bindClickableRail: function () {
                this._dd.addHandle( this.rail );

                this.rail.on( this._evtGuid + 'mousedown',
                    this._onRailMouseDown, this );
            },

            /**
             * Detaches DOM event subscribers for cleanup/destruction cycle.
             *
             * @method _unbindClickableRail
             * @protected
             */
            _unbindClickableRail: function () {
                if ( this.get( 'rendered' ) ) {
                    var contentBox = this.get( 'contentBox' ),
                        rail = contentBox.one( '.' + this.getClassName( 'rail' ) );

                    rail.detach( this.evtGuid + '*' );
                }
            },

            /**
             * Dispatches the railMouseDown event.
             *
             * @method _onRailMouseDown
             * @param e {DOMEvent} the mousedown event object
             * @protected
             */
            _onRailMouseDown: function ( e ) {
                if ( this.get( 'clickableRail' ) && !this.get( 'disabled' ) ) {
                    this.fire( 'railMouseDown', { ev: e } );
                }
            },

            /**
             * Default behavior for the railMouseDown event.  Centers the thumb at
             * the click location and passes control to the DDM to behave as though
             * the thumb itself were clicked in preparation for a drag operation.
             *
             * @method _defRailMouseDownFn
             * @param e {Event} the EventFacade for the railMouseDown custom event
             * @protected
             */
            _defRailMouseDownFn: function ( e ) {
                e = e.ev;

                // Logic that determines which thumb should be used is abstracted
                // to someday support multi-thumb sliders
                var dd     = this._resolveThumb( e ),
                    i      = this._key.xyIndex,
                    length = parseFloat( this.get( 'length' ), 10 ),
                    thumb,
                    thumbSize,
                    xy;

                if ( dd ) {
                    thumb = dd.get( 'dragNode' );
                    thumbSize = parseFloat( thumb.getStyle( this._key.dim ), 10);

                    // Step 1. Allow for aligning to thumb center or edge, etc
                    xy = this._getThumbDestination( e, thumb );

                    // Step 2. Remove page offsets to give just top/left style val
                    xy = xy[ i ] - this.rail.getXY()[i];

                    // Step 3. Constrain within the rail in case of attempt to
                    // center the thumb when clicking on the end of the rail
                    xy = Math.min(
                            Math.max( xy, 0 ),
                            ( length - thumbSize ) );

                    this._uiMoveThumb( xy );

                    // Delegate to DD's natural behavior
                    dd._handleMouseDownEvent( e );
                }
            },

            /**
             * Resolves which thumb to actuate if any.  Override this if you want to
             * support multiple thumbs.  By default, returns the Drag instance for
             * the thumb stored by the Slider.
             *
             * @method _resolveThumb
             * @param e {DOMEvent} the mousedown event object
             * @return {Y.DD.Drag} the Drag instance that should be moved
             * @protected
             */
            _resolveThumb: function ( e ) {
                var primaryOnly = this._dd.get( 'primaryButtonOnly' ),
                    validClick  = !primaryOnly || e.button <= 1;

                return ( validClick ) ? this._dd : null;
            },

            /**
             * Calculates the top left position the thumb should be moved to to
             * align the click XY with the center of the specified node.
             *
             * @method _getThumbDestination
             * @param e {DOMEvent} The mousedown event object
             * @param node {Node} The node to position
             * @return {Array} the [top, left] pixel position of the destination
             * @protected
             */
            _getThumbDestination: function ( e, node ) {
                var offsetWidth  = node.get( 'offsetWidth' ),
                    offsetHeight = node.get( 'offsetHeight' );

                // center
                return [
                    ( e.pageX - Math.round( ( offsetWidth  / 2 ) ) ),
                    ( e.pageY - Math.round( ( offsetHeight / 2 ) ) )
                ];
            }

        },

        // Static properties added onto host class
        ATTRS: {
            /**
             * Enable or disable clickable rail support.
             *
             * @attribute clickableRail
             * @type {Boolean}
             * @default true
             */
            clickableRail: {
                value: true,
                validator: Y.Lang.isBoolean
            }
        }

    }, true );

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