Is this recursion or not

Question

function x(){
  window.setTimeout(function(){
     foo();
     if(notDone()){ 
        x();
     };
  },1000);
}

My concern being unbounded stack growth. I think this is not recursion since the x() call in the timer results in a brand new set of stack frames based on a new dispatch in the JS engine.

But reading the code as an old-fashioned non JS guy it makes me feel uneasy

One extra side question, what happens if I scheduled something (based on math rather than a literal) that resulted in no delay. Would that execute in place or would it be in immediately executed async, or is that implementation defined

Answer 1

It's not - I call it "pseudo-recursion".

The rationale is that it kind of looks like recursion, except that the function always correctly terminates immediately, hence unwinding the stack. It's then the JS event loop that triggers the next invocation.

Answer 2

It is recusive in a sense that it is a function that calls itself but I believe you are right about the stack trace being gone. Under normal execution the stack will just show that it was invoked by setTimeout. The chrome debugger for example will allow you to keep stack traces on async execution, I am not sure how they are doing it but the engine can keep track of the stack somehow.

No matter how the literal is calculated the execution will still be async.

setTimeout(function(){console.log('timeout');}, 0);console.log('executing');

will output:

executing
undefined
timeout