You need to include jquery first. Use this to code to include jquery require(['jquery'], function($){ //your code to send ajax request here

$.ajax({ showLoader: true, url: "admin/PostaPlus/PostaPlusShipping/HSCodes", data: param, type: "POST",

dataType: 'json' }).done(function (data) { alert(data); console.log(data); });

Here is my custom controller codes,

});

You need to include jquery first. Use this to code to do it:

require([
    "jquery"
], function ($) {
     //your code to send ajax request here
    $.ajax({
        showLoader: true, 
        url: "admin/PostaPlus/PostaPlusShipping/HSCodes", 
        data: param,
        type: "POST", 
        dataType: 'json'
    }).done(function (data) { 
        alert(data); console.log(data); 
    });
});