There are actually a few implementations of this for JS, it is an approach that Crockford has championed quite a bit (e.g https://plus.google.com/+DouglasCrockf

There are actually a few implementations of this for JS, it is an approach that Crockford has championed quite a bit (e.g https://plus.google.com/+DouglasCrockfordEsq/posts/XXkzgJEoE9v https://plus.google.com/+DouglasCrockfordEsq/posts/XXkzgJEoE...). Some implementations that I'm aware of, there may be others: * http://www.vim.org/scripts/script.php?script_id=4748 http://www.vim.org/scripts/script.php?script_id=4748 * https://github.com/mazurov/sublime-levels https://github.com/mazurov/sublime-levels * https://github.com/daniellmb/JavaScript-Scope-Context-Coloring https://github.com/daniellmb/JavaScript-Scope-Context-Colori...