I had to take a few steps back and get to know Javascript better. I started with a completely blank HTML5 canvas, and worked my way up slowly. Debugging Javascript is hard. Google Chrome's development tool really just tells you when there's an error - what I really need is a step-through debugger AND a profiler. Anyway, I battled on, sprinkling alert() like printf()s. One of the annoying things about Javascript is that when it fails it doesn't throw an error message, it just quietly gives up. Sometimes I didn't even realise when an error had occured. Chrome was good for this.
File I/O is a bit wonky in Javascript. Everything is web-based, of course, so you use a method called Ajax (Asynchronous Javascript And XML) to make a standard HTML GET request for your file. It doesn't have to be asynchronous, and it doesn't have to be XML. The trick to Ajax is that when you get the file returned from the request, it fires a little callback function that you write to parse the file. In asynchronous mode it may take some time before your function is called. I forgot about this and it gave me the weirdest problems later on. The trick was to turn off asynchronous callbacks - making the programme wait at that line before running any other code.
Parsing flat files in Javascript is every bit as long-winded and disgusting as doing it with C. You don't have a scanf() function, but you can parse using regular expressions. This means that your old plain text files are no longer ideal, and the parsing code is even longer and uglier. You could rewrite your files to something more suited to regular expression matching, but Javascript has its own format called JSON (Javascript Object Notation). JSON is excellent. In my opinion much nicer than using XML to construct an object. Rewrite your plain text in JSON format and then it's only one, mindless function call to set all the attributes of your object. Done.
Familiarise more with drawing objects in WebGL. Build up the shader object (not class) or shader manager mentioned last time. I can see now why it's very handy to have things like .obj meshes converted into JSON format first.