Deeply frozen data is a good middle ground to have immutability without Immutable.js: during development, automated tests can catch code that would attempt to

Deeply frozen data is a good middle ground to have immutability without Immutable.js: during development, automated tests can catch code that would attempt to mutate, and you have the option to remove the deep freezing in the release version to have no runtime penalty once you're confident that nothing can mutate the data.