How can I open data/data/com.termux/files

In order to get to the Termux files folder, you have to CD to the entire path name like this.

cd /data/data/com.termux/files

From there can cd into the usr folder and where ever you want to go. Once you find writer.js you can edit it using nano which comes with Termux. Enter nano writer.js, make your edits and the use CTRL O to save it and CTRL X to exit nano.

Then you can get back to your home directory with:

cd ~