On the mobile device, the 'expandMode' can be set to 'float' and the 'collapsedSize' can be set to '0' to hide the collapsed bar.
<div data-options="region:'west',split:true,border:false,expandMode:'float',hideExpandTool:true,collapsedSize:0" title="west" style="width:150px;">
...
</div>
Call this code to collapse the west panel.
$(...).layout('expand','west');
Call this code to expand the west panel.
$(...).layout('panel','expandWest').trigger('click');