JSFiddle - React, Tailwind, and code Playground

HTML

<div id=sample>This is a script that would be useful to run within other functions</div>

JavaScript

$( document ).ready(function() {
// Also note, that for $('#sample').myplugin() to work
// you need the element with id "sample" to be existent
// so the function is actually called
(function($){
  $.fn.myplugin = function(){
    // in your code, the `this` is pointing to 
    // jQuery object, you can't access `id` attribute
    // with dot. You need to either access first element
    // in jQuery object (`this[ 0 ]`) or use this.attr('id')
    // alert( this[0].id );
    alert( "This element has an id of #'"+this[0].id+"'! After closing this, click the paragraph to bring this alert back." );
  };
})(jQuery);

$( "#sample" ).click(function() {
  $( this ).myplugin();
});

$("#sample").myplugin();

});