The HTML5 specifications states that setTimeout can be run without the additional "timeout" argument which is supposed to say after how many milliseconds will the function "handler" be scheduled.

handle = window . setTimeout( handler [, timeout [, arguments ] ] )
   Schedules a timeout to run handler after timeout milliseconds. Any arguments are passed straight through to the handler.

However, I failed to find anywhere which explains what happens when no "timeout" time period is set.

An example usage is, the animation implementation int the Raphael library.

animationElements[length] && win.setTimeout(animation);

The HTML5 specifications states that setTimeout can be run without the additional "timeout" argument which is supposed to say after how many milliseconds will the function "handler" be scheduled.

handle = window . setTimeout( handler [, timeout [, arguments ] ] )
   Schedules a timeout to run handler after timeout milliseconds. Any arguments are passed straight through to the handler.

However, I failed to find anywhere which explains what happens when no "timeout" time period is set.

An example usage is, the animation implementation int the Raphael library.

animationElements[length] && win.setTimeout(animation);

• javascript
• settimeout

• All current major browsers are able to accept a single argument, so to avoid any confusion it's worth pointing out that a browser does not have to be HTML5 pliant to support this. – Andy E Commented Apr 27, 2010 at 18:09
• 2 This is a splendid way of doing deferred procedure calls in JS - "do X later/not-right-now". If you're inside an event handler, it may be a bad time to call some function because of state/re-entrancy issues. Note that you cannot guarantee the actual execution time, but it's "soon". – JBRWilkinson Commented Apr 27, 2010 at 18:28
• @Andy Mozilla MDC states the millisecond as a mandatory parameter. – Elazar Leibovich Commented Apr 27, 2010 at 18:34
• @JBRWilkinson: Indeed, and it's also a great way to delay execution with the possibility of cancelling it if a particular event fires. I've used this technique numerous times and it's really useful. – Andy E Commented Apr 27, 2010 at 19:02
• Related: Why is setTimeout(fn, 0) sometimes useful?, NodeJS - setTimeout(fn,0) vs setImmediate(fn). – Sebastian Simon Commented Sep 25, 2021 at 16:56

1 Answer 1

See http://www.whatwg/specs/web-apps/current-work/multipage/timers.html#get-the-timeout

1. Let timeout be the second argument to the method, or zero if the argument was omitted.