Question

Say I have some code:

setInterval(foo,1000); // here is an interval that causes a function to repeat

function foo(){
//a number of lines of code
}

Now, i think of this as causing foo() to be executed every second by the system clock, whereas this:

function foo(){
//a number of lines of code
setTimeout(foo,1000);    } //here is a timeout that causes the function to repeat

Am I correct in guessing that the latter function would be executed less often in a given period of time, because I’m inserting a pause between executions (which, themselves, take a measurable amount of time)? Any further points or enlightenment on this mechanism would be welcomed.

Answer 1

Let me quote an article about timers by John Resig, which specifically addresses your question:

setTimeout(function(){
  /* Some long block of code... */
  setTimeout(arguments.callee, 10);
}, 10);

setInterval(function(){
  /* Some long block of code... */
}, 10);

These two pieces of code may appear to
be functionally equivalent, at first
glance, but they are not. Notably the
setTimeout code will always have at
least a 10ms delay after the previous
callback execution (it may end up
being more, but never less) whereas
the setInterval will attempt to
execute a callback every 10ms
regardless of when the last callback
was executed.

Intervals may execute back-to-back with no delay if they take long enough to execute (longer than the specified delay).

Keep also in mind that accuracy of JavaScript timers differs between browsers and platforms.