This is (to respond to sibling comments) not the halting problem per se. It is the problem of not having any control over a runaway loop in the browser. You cou

This is (to respond to sibling comments) not the halting problem per se. It is the problem of not having any control over a runaway loop in the browser. You could parse and transform code to add a check on every backwards jump (end of loop body, continue statements) that increments a counter or checks the time and throws an exception when it decides the code has ran for too long. (Of course, that'll slow the code down a lot.)