It is a shrinker/obfuscator for JavaScripts. You can use it to easily and quickly reduce the size of typical JavaScript files by 50% on average depending on the style the code is written in. Strong JS allows you to delete all unnecessary bytes in scripts, such as comments, new line characters and unnecessary spaces. The execution of the js file won't change after it is compressed. It just executes like before. You won't see a difference, only the file size will be smaller. Also, it can rename variables giving them short names. Shrinking JavaScripts reduces the time they are downloaded from the site and the time needed to parse and execute them on the client side.