This is the source code of a chrome extension that disables read receipts and presence updates on WhatsApp Web. You can find the original extension in Chrome Web Store.
To install the extension off-store, download the latest release as a zip file from the Releases page, extract its content to a directory and add it to Chrome using the 'Load unpacked extension' option when developer mode is turned on.
This extension works by intercepting the WebSocket frames between chrome and WhatsApp's servers using a modified WebSocket constructor (see wsHook).
Those frames are then decrypted if needed using the local encryption keys (stored in localStorage), and decoded from a binary form using a javascript code from WhatsApp's original implementation.
The resulting "nodes" are then simply checked to see if WhatsApp tries to send out a read or presence action, and if so, the extension blocks it and fakes a failure response from the server.
The main code of the extension is located in core/Main.js and core/UI.js.
Other files inside the core folder deal with the infrastructure that makes the interception and the decoding works. There is also an additional code for parsing messeges (such as MessageTypes.js) that is not used in the extension.
background.js mainly keeps track of the saved prefrences using localStorage.
If you want to see what kind of messages WhatsApp is sending and receiving over WebSocket in real-time, you can type WAdebugMode = true in the javascript console. Incoming and outgoing payloads (after decryption) will be printed out.
No data is ever transmitted to anywhere. Privacy policy here.