Get difference between html code rather than content

[Hanzla-Double3]

I am trying to build a note taking app, but i want to calculate the changes that has been made since last saved. I want html content rather than just the text content. It does send attributes changes back to server but I am too lazy to create a logic for that, cuz i have some custom tags too. So if someone know how to get difference without using any other third party script, lemme know
Thank you for your time