getPrevSiblingId

returns the id of the previous sibling of the specified node

id getPrevSiblingId(id id);

ID of the node in question

id	ID of the previous sibling or false if there isn't any

Example

tree = webix.ui({
    view:"tree",
    data: [
        { id:"branch1", value:"The Shawshank Redemption", data:[
            { id:"part1", value:"Part 1" },
            { id:"part2", value:"Part 2" }
        ]}
    ]
});
 
tree.getPrevSiblingId("part2"); // returns 'part1'