I've been working on something similar for teaching graphics programming to our undergrads. Uses esprima to parse the input JS and add some runtime error checking with line numbers, including unidentified variables and timeouts for loops:
I will always remember what Bret Victor said about these kinds of projects in his Learnable Programming essay:
> As you can see, live coding, on its own, is almost worthless. The programmer still must type at least a full line of code before seeing any effect. This means that she must already understand what line of code she needs to write. The programmer is still doing the creative work entirely in her head -- imagining the next addition to the program and then translating it into code.
(To be fair to yaxu, its not live coding that he is talking about, but the feature of live update in isolation.)
Simpsons already did it. Well OK, @sanchothefat already did a similar thing using Processing.js over at http://hascanvas.com - bit old now but he had plenty of interesting user contributions over the years.
I like this. I have worked on a couple of things in a similar area.
This too suffers from the problem that has plagued me.
I tried to add this code to the program
var x=2;
var y=1;
while (x>y) {
x+=2;
y+=1;
}
Which is my usual check for what happens when you encounter an endless loop.
Of course, I didn't get the entire thing typed in because the user interface froze when I typed the close bracket of (x>y).
Javascript can't pre-empt. An endless loop is a killer. I'm going to write something long and detailed about this one day. It'll be a big rant.
I made a MediaWiki plugin for my approach. It uses a worker, which lets you do something about busy loops (you can kill it, not much else). The down side is that all of the drawing operations have to be passed through to the host as messages.
The other part of what I have been working on is a extremely simple API to use environments like this for novice programmers.
I teach some programming in a class of 10 year olds. I start off with
http://jsbin.com/tinydraw/1/edit
Which is a program they can focus on in one view and lets them draw pictures.
Then I make suggestions and point them to the wiki. Where they go from there is amazing to see.
I like this one. Here a kid figured out from the wiki how to read the mouse.
http://jsbin.com/tinydraw/50/edit Scattered through the versions are evolutions of this program until it ends up here, as a simple, but fairly complete game. http://jsbin.com/tinydraw/141/edit
