Javascript or Extendscript

Javascript and Extendscript are the two lanaguges expression can be written in. I will always recommend writing expressions in javascript and not extendscript.

Javascript

Javascript was recently introduced with After Effects CC2019, this now means expressions can handle modern javascript methods allowing them to do much more complex things with alot more ease. This means for the daily user expression are MUCH MUCH quicker, they also have become a lot shorter! Less lines to read means more time to render *this might not be true

Extendscript

Extendscipt is the original expression engine used in After Effects. It's now moved into the category of legacy. It has less functionality than modern day javascript and is much much slower.

Compatibility Issues

Javascript and Extendscript are not exactly compatible with eachother. The newer javascript methods do not work with extendscript The older extendscript writing methods no longer work in javascript