Did you try looking in the manual?
construct.net/en/make-games/manuals/construct-3/scripting/using-scripting/script-files
Adding script files
Script files can be added in the Scripts folder of the Project Bar. Existing JavaScript files (.js) can also be imported using the Import scripts option instead.
Factorio uses zlib for compression of json data, similar to what you're trying to achieve.
A blueprint string is a JSON representation of the blueprint, compressed with zlib deflate using compression level 9 and then encoded using base64 with a version byte in front of the encoded string. The version byte is currently 0 (for all Factorio versions through 1.1). So to get the JSON representation of a blueprint from a blueprint string, skip the first byte, base64 decode the string, and finally decompress using zlib inflate.
Here is a javascript implementation of zlib
github.com/imaya/zlib.js/blob/develop/README.en.md
I think you're better off using pastebin like what dop suggested or trimming the fat out of the data as rojo said, basically make your own file format. Doing so really depends on the amount and type of data specific to your game though.