Babel plugins run order

The order of plugins is based on the order of things in your .babelrc with plugins running before presets, and each group running later plugins/presets before earlier ones.

The key thing though is that the ordering is per AST Node. Each plugin does not do a full traversal, Babel does a single traversal running all plugins in parallel, with each node processed one at a time running each handler for each plugin.

Basically, what @loganfsmyth wrote is correct; there is (probably) no more magic in plugin ordering itself.

As for the my problem specifically, my confusion was caused by how arrow function transformation works. Even if the babel-plugin-transform-es2015-arrow-functions plugin mangles the code sooner than my plugin, it does not remove the original arrow-function ast node from the ast, so even the later plugin sees it.

Learning: when dealing with Babel, don't underestimate the amount of debug print statements needed to understand what's happening.