sets an action happening on a button click
{ view:"button", value: "Submit", click:function(){....} }
The click property may have the function as value as well as the name of this function.
{ view:"button", value: "Submit", click:filter_tree}
function filter_tree(){
$$("tree1").filter("#value#", this.getValue());
}
The property is used with a JS button only, while other components have "onItemClick" inner event to respond to this mouse action.