how to get started from 0 knowneldge of javascript and web apis ?

[evanescente-ondine]

Hi,
Someone that was close to me died and left me with a project to develop and carry to completion.
I have to make a quick typing course program in the form of a website. Concretely the only thing that I haven't been able to do so far, is an automatic correction by aligning the user input (in a contenteditable element) to a model.
Coming from Ada, I find JavaScript impossibly abstruse, really horrible, and the separation of what I need to know between apis and the language itself doesn't help. I don't know where to start.
Logically, what I imagine doesn't seem too complicated: at each input event in the element, 300ms after input ended, compare the last visible character before the caret with the one of the model at the same offset, and trigger some alarm if it doesn't match.
I could use a more elaborate alignment taking insertions and deletions into accounts but it matters less, people aren't supposed to continue writing after the alarm buzzes.
So, what would be the best course of action for me ?