implement an external library e.g. context menu

Going further with my project i want to implement context menu functionality!
Therefore i downloaded a library from https://swisnl.github.io/jQuery-contextMenu/

i included it in my default.js file in .../apps/assets/scripts like

EasySocial.require()

.library('ui/resizable', 'ui/draggable', 'ui/selectable', 'moment')

.script(''<?php echo rtrim( JURI::root() , '/' );?>/media/com_easysocial/apps/group/planner/assets/scripts/context-menu/src/jquery.contextMenu.js',

        '<?php echo rtrim( JURI::root() , '/' );?>/media/com_easysocial/apps/group/planner/assets/scripts/context-menu/screen.js',

        '<?php echo rtrim( JURI::root() , '/' );?>/media/com_easysocial/apps/group/planner/assets/scripts/context-menu/prettify/prettify.js').done(function($) {

$.contextMenu({

    selector: 'span.context-menu'

});

}

But mixing external libraries with ES seems not quite easy!
By running the script above it gives me

TypeError: $.contextMenu is not a function

Do i have to adapt external libraries for using in ES?

Thanks and good morning from Vienna