A useful site which creates a spite with flags and accompanying CSS classes to use. www.flag-sprites.com
Javascript Object Comparison https://stamat.wordpress.com/2013/06/22/javascript-object-comparison/
REACT lifecycle hooks explained http://busypeoples.github.io/post/react-component-lifecycle
JavaScript Kit - (free scripts) http://www.javascriptkit.com/
Progress bars / loading bars to plugin. https://www.freshdesignweb.com/jquery-css3-loading-progress-bar/
CSS spacing elements equally https://css-tricks.com/equidistant-objects-with-css/
CSS progress bar design https://css-tricks.com/css3-progress-bars/
CSS flexbox https://learnlayout.com/flexbox.html and https://css-tricks.com/snippets/css/a-guide-to-flexbox/
Font stack and other tools Dan's Tools for web design
Node JS Shopping Cart Tutorial YouTube playlist uses Express Generator
Recursion explained https://www.khanacademy.org/computing/computer-science/algorithms/recursive-algorithms/a/recursion
JS escape characters http://www.c-point.com/javascript_tutorial/special_characters.htm