JSFiddle - React, Tailwind, and code Playground

JavaScript

(function( $ ){
    $.fn.x = function(option) {
        var def = {
            a: 1,
            b: 2
        };

        option = $.extend(def, option);
        function abc() {
            console.log( 'Plugin method called' );
        }
        function def() {
            //do something
        }
    };
})( jQuery );

(function(){
    var _x = $.fn.x;
    $.fn.x.abc = function() {
        console.log( 'Overidden method called' );
        _x.abc.apply( this, arguments );
    }
})();

(function() {
    $.fn.x.abc();
});