This is a CodeMirror mode that provides syntax highlighting for variables in arbitrary contexts (e.g. variables that appear in a string for later interpolation).
Load variables.js at an adequate location in your HTML structure.
Mention mode: 'variables' when creating your CodeMirror instance.
By default, codemirror-mode-variables highlights basic shell-like variables like $foo and ${bar}.
It supports custom variable patterns and the CodeMirror tokens it returns can be customised too. Refer to the demo page for further explanations.
Unless customised, this mode leverages CodeMirror's default tokens and should therefore fit in with all CodeMirror themes.
codemirror-mode-variables can be nested within another mode, i.e. it can highlight variables for another mode. This requires adjusting the other mode though. See the demo page for an example of such nesting.
This mode is released under the 3-clause BSD license.