Keyboard mixin throws TypeError

[zub2]

The moveFocusHorizontal and moveFocusVertical in Keyboard mixin throw TypeError (or pass undefined to Grid.prototype.up/down/left/right which then throw TypeError) when the List or Grid contain fewer items than what would fill the whole height of the table.

If the List or Grid are completely empty (the collection they render contains 0 items), then pressing any arrow or pg up/down keys results in the TypeError for both List + Keyboard and Grid + Keyboard (both cellNavigation true and false).

If the List or Grid are not empty, but there is an unused space at the bottom (e.g. the list contains only 1 item, but the height is so that there is unused space below the item), then the TypeError is thrown only for Grid + Keyboard case, with cellNavigation true. This happens when user clicks in the empty area and then presses any arrow or pg up/down. For cellNavigation false, the arrows or pg up/down just bring the focus back to one of the existing elements.

I'm seeing this issue with DGrid 1.1.0 with Firefox 45.2.0 and Chrome 52.0.2743.82.

To reproduce with the official tests:

Issue with empty grid/list:

1. edit test/data/genericData.js: change line 20 to: var rows = 0;
2. display test/Keyboard.html in browser
3. click in one of the three empty grid displayed to focus them
4. press one of arrow left/right/up/down or page up/down
5. look into browser JS log - there are TypeErrors logged

Issue with few items:

1. edit test/data/genericData.js: change line 20 to: var rows = 3;
2. display test/Keyboard.html in browser
3. click in the empty space in the middle grid (Grid + Keyboard + cellNavigation true) to focus the grid
4. press one of arrow left/right/up/down or page up/down
5. look into browser JS log - there are TypeErrors logged

[zub2]

Clarification: It seems that left/right arrows only cause an exception for Grid + Keyboard + cellNavigation true + tabableHeader: false.

This can be reproduced by editing the middle grid in test/Keyboard.html, e.g.:

                    grid = window.grid = new KeyboardGrid({
+                       tabableHeader: false,
                        collection: testStore,
                        columns: columns
                    }, "grid"),

For tabableHeader: true, left/right arrow just focus the header w/o any error. And left/right arrows for List + Keyboard and Grid + Keyboard + cellNavigation false do nothing, and don't trigger an error.