Icons can be used for nodes as well. This example shows Icons from fontAwesome and Ionicons but it should work with similar packages as well. It uses unicode and css to define the icons.

Remember! Unicode in javascript is done like this: \uf274 for the unicode f274.
If a node is shown as a rectangle, it means the css is not loaded (or not yet loaded). A redraw will fix that.

Use FontAwesome-icons 4 for nodes

Use FontAwesome-icons 5 for nodes

Use Ionicons-icons for nodes