Terminate loops after 1s timeout or 10,000 iterations

[wylieconlon]

This is a fix for popcodeorg/popcode#1354, "Loop breaking doesn't work if there's a console.log() in the loop body"

[wylieconlon]

I updated the code to sample every 100 loops

[wylieconlon]

@outoftime Looking for a review on this

[outoftime]

@wylieconlon so I don’t have any particular objection to this, but it doesn’t appear to solve the original issue—a loop with a lot of console.log statements still locks up the environment. Doesn’t have to be an infinite loop at all; a simple count up to 10,000 does the trick quite nicely.

I suspect this has to do with the way the JavaScript execution is scheduled between Popcode itself (window.top) and the preview frame. Each time console.log() is called, it’s sending a postMessage up to window.top which causes an excessively expensive Redux update (particularly when performed in a tight loop). Once the top-level execution frame starts chugging, that takes priority over the execution of the loop (and the loop breaker) in the iframe. A couple years ago I did some experimentation and found evidence that browsers (at least Chrome) prioritize JavaScript execution in the top-level window over execution in iframes (which also makes intuitive sense).

Anyway, I pushed this to version 0.1.1-alpha.1 on npm, so feel free to install it in your local Popcode environment and mess around with it. LMK if you think it’s still worth merging!