For this error, jQuery version doesn't matter, this error could be thrown if the code from that demo is used in pqgrid free version
Please ensure that you are using Pro latest version.
Thanks. I believe I am using the Pro latest version.
I don't know what happened. I modified the code as below
var $toolbar = $grid.find('.pq-toolbar'),
//var $toolbar = this.toolbar(),
var grid = $grid.pqGrid("instance");
grid.filter({
//this.filter({
and it is working now.