Codemods and Code Refactoring

Codemod (opens in a new tab) was a tool/library developed by FaceBook to assist with large-scale codebase refactors that can be partially automated but still require human oversight and occasional intervention. It is now deprecated and archived.

Code refactoring (opens in a new tab) is the process of restructuring existing computer code—changing the factoring—without changing its external behavior.

Example:

Let's say you're deprecating your use of the <font> tag. From the command line, you might make progress by running:

codemod -m -d /home/jrosenstein/www --extensions php,html \
    '<font *color="?(.*?)"?>(.*?)</font>' \
    '<span style="color: \1;">\2</span>'

For each match of the regex, you'll be shown a colored diff, and asked if you want to accept the change (the replacement of the <font> tag with a <span> tag), reject it, or edit the line in question in your $EDITOR of choice.

Codemods are scripts used to rewrite other scripts. Think of them as a find and replace functionality that can read and write code. You can use them to

update source code to fit a team’s coding conventions,
make widespread changes when an API is modified, or
even auto-fix existing code when your public package makes a breaking change.
etc.

Recast Jscodeshift