function handler()

in adminlte/html/plugins/select2/js/select2.full.js [6613:6724]
77 lines of code
28 McCabe index (conditional complexity)

    function handler(event) {
        var orgEvent   = event || window.event,
            args       = slice.call(arguments, 1),
            delta      = 0,
            deltaX     = 0,
            deltaY     = 0,
            absDelta   = 0,
            offsetX    = 0,
            offsetY    = 0;
        event = $.event.fix(orgEvent);
        event.type = 'mousewheel';

        // Old school scrollwheel delta
        if ( 'detail'      in orgEvent ) { deltaY = orgEvent.detail * -1;      }
        if ( 'wheelDelta'  in orgEvent ) { deltaY = orgEvent.wheelDelta;       }
        if ( 'wheelDeltaY' in orgEvent ) { deltaY = orgEvent.wheelDeltaY;      }
        if ( 'wheelDeltaX' in orgEvent ) { deltaX = orgEvent.wheelDeltaX * -1; }

        // Firefox < 17 horizontal scrolling related to DOMMouseScroll event
        if ( 'axis' in orgEvent && orgEvent.axis === orgEvent.HORIZONTAL_AXIS ) {
            deltaX = deltaY * -1;
            deltaY = 0;
        }

        // Set delta to be deltaY or deltaX if deltaY is 0 for backwards compatabilitiy
        delta = deltaY === 0 ? deltaX : deltaY;

        // New school wheel delta (wheel event)
        if ( 'deltaY' in orgEvent ) {
            deltaY = orgEvent.deltaY * -1;
            delta  = deltaY;
        }
        if ( 'deltaX' in orgEvent ) {
            deltaX = orgEvent.deltaX;
            if ( deltaY === 0 ) { delta  = deltaX * -1; }
        }

        // No change actually happened, no reason to go any further
        if ( deltaY === 0 && deltaX === 0 ) { return; }

        // Need to convert lines and pages to pixels if we aren't already in pixels
        // There are three delta modes:
        //   * deltaMode 0 is by pixels, nothing to do
        //   * deltaMode 1 is by lines
        //   * deltaMode 2 is by pages
        if ( orgEvent.deltaMode === 1 ) {
            var lineHeight = $.data(this, 'mousewheel-line-height');
            delta  *= lineHeight;
            deltaY *= lineHeight;
            deltaX *= lineHeight;
        } else if ( orgEvent.deltaMode === 2 ) {
            var pageHeight = $.data(this, 'mousewheel-page-height');
            delta  *= pageHeight;
            deltaY *= pageHeight;
            deltaX *= pageHeight;
        }

        // Store lowest absolute delta to normalize the delta values
        absDelta = Math.max( Math.abs(deltaY), Math.abs(deltaX) );

        if ( !lowestDelta || absDelta < lowestDelta ) {
            lowestDelta = absDelta;

            // Adjust older deltas if necessary
            if ( shouldAdjustOldDeltas(orgEvent, absDelta) ) {
                lowestDelta /= 40;
            }
        }

        // Adjust older deltas if necessary
        if ( shouldAdjustOldDeltas(orgEvent, absDelta) ) {
            // Divide all the things by 40!
            delta  /= 40;
            deltaX /= 40;
            deltaY /= 40;
        }

        // Get a whole, normalized value for the deltas
        delta  = Math[ delta  >= 1 ? 'floor' : 'ceil' ](delta  / lowestDelta);
        deltaX = Math[ deltaX >= 1 ? 'floor' : 'ceil' ](deltaX / lowestDelta);
        deltaY = Math[ deltaY >= 1 ? 'floor' : 'ceil' ](deltaY / lowestDelta);

        // Normalise offsetX and offsetY properties
        if ( special.settings.normalizeOffset && this.getBoundingClientRect ) {
            var boundingRect = this.getBoundingClientRect();
            offsetX = event.clientX - boundingRect.left;
            offsetY = event.clientY - boundingRect.top;
        }

        // Add information to the event object
        event.deltaX = deltaX;
        event.deltaY = deltaY;
        event.deltaFactor = lowestDelta;
        event.offsetX = offsetX;
        event.offsetY = offsetY;
        // Go ahead and set deltaMode to 0 since we converted to pixels
        // Although this is a little odd since we overwrite the deltaX/Y
        // properties with normalized deltas.
        event.deltaMode = 0;

        // Add event and delta to the front of the arguments
        args.unshift(event, delta, deltaX, deltaY);

        // Clearout lowestDelta after sometime to better
        // handle multiple device types that give different
        // a different lowestDelta
        // Ex: trackpad = 3 and mouse wheel = 120
        if (nullLowestDeltaTimeout) { clearTimeout(nullLowestDeltaTimeout); }
        nullLowestDeltaTimeout = setTimeout(nullLowestDelta, 200);

        return ($.event.dispatch || $.event.handle).apply(this, args);
    }