I once had similar requirement, so I actually used Search result
webpart, but you can check below code for Content Search
webpart as well.
Code is somewhat different for Content Search
webpart, which you can check by this good article.
I had one site drop-down, list drop-down, keyword text-box and next to that search button which will search the result dynamically.
Below is the jquery
code for on change event for site drop-down on content search that you can use:
// Attach change event handler to Site dropdown
$('#drpSites').change(function () {
// Get selected product ID
var sites = $(this).val();
// Loop through Query Groups
var groups = Srch.ScriptApplicationManager.get_current().queryGroups;
$.each(groups, function () {
// Look for query groups associated with a CSWP
if (this.displays != null && this.displays.length > 0) {
if (this.displays[0] instanceof Srch.ContentBySearch) {
// Update and execute query
var newQuery = 'contentType:Orders sites:' + prd;
this.dataProvider.set_queryTemplate(newQuery);
this.dataProvider.issueQuery();
}
}
});
});
So for your termset you can enter your query in newQuery
variable to fetch data accordingly.
Hope this helps!