How to read and write a file through dom js

I meant to put I can't post the image but here is the image of what I am working on https://i.stack.imgur.com/qj5H2.png. I would like to store some data on the file all.txt(ex. Passwods and usernames, form submission,ect.). However I would like to read and write on that file with dom java script. How would I do that? enter image description here