setInterval and long running functions

问题:

How does setInterval handle callback functions that take longer than the desired interval?

I've read that the callback may receive the number of milliseconds late as its first argument, but I was unable to find why it would be late (jitter, or long running functions).

And the wonderful follow up, does it behave differently for the common browsers?

回答1:

Let me quote an excellent article about timers by John Resig:

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).