They don't. The program runs in your browser. It isn't their problem if it contains an infinite loop. If the page stops responding, you simply reload the page.
Programming contests use a check program that has a time limit on program execution.
Programming contests use a check program that has a time limit on program execution.
while(true){}
the page loads but the ide says time limit exceeded after 5 seconds and stops the execution. Now, how do you do that?
executeUserProgram(userProgram, timeout=5)...
Both approaches look for the effects of an infinite loop instead of the program logic of an infinite loop. Which makes sense since logical analysis for infinite loops is the Halting Problem and NP-Hard.
executeUserProgram()