Learn about our RFC process, Open RFC meetings & more.Join in the discussion! »


0.1.9 • Public • Published


Start with a short time limit and extend it dynamically.

Can be used to recover from broken callback chains that stop unexpectedly. Start with a very short timeout, so you're notified when your function just forgets to call back. The short limit won't be a problem for functions aware of it, because they can dynamically extend/renew it.

Additional features:

  • Helps you determine which function timed out.


This module exports one function:

callbackTimeoutFlexible(origCb, timeoutSec)

Immediately starts a timeout timer, then returns a timeout-aware callback (proxy) function prx. When prx is called within timeoutSec seconds, it schedules function origCb to be called very soon, with the same arguments that were passed to prx. (this context is not preserved.)

When the timeout expires before prx is invoked, origCb will be called with one argument, an Error that describes which timeout has expired. (Or whatever opt.errFac returned, see below.) The default error factory uses 'TimeoutError' as the error's .name.

There's a timeout control object (TCO) in prx.timeout which allows to extend the timeout (see below).

timeoutSec can be a config object instead of a number, with these options:

Mandatory options:

  • limitSec: Timeout in seconds. Expected to be a positive number.

Optional options:

  • name: A custom name for this timeout, to be used in or as its description.
  • onLateCall: What to do when prx is called after origCb has already been notified, either because of a previous prx invocation, or because the timeout has expired.
    • any false-y value: Don't notify. Discard the arguments.
    • true: Forward the invocation to origCb.
    • any function: Forward the invocation to that function.
  • onBeforeTimeout: A function to be called (with one argument: the TCO) just before origCb would be called with a timeout error. It's intended as a last-minute opportunity to extend the timeout.
  • startTime: Set to true to request timestamps.
  • errFac: Factory function to use for producing the timeout errors.
  • errMsg: Template string for the default error factory's error messages. Supports these variable slots:
    • \v{name}: tco.name
    • \v{this}: String(tco)
  • autostart: If set to false, timers won't be started immediately.
  • unref: Set to true if timers shall be .unref()ed.
    • The Node.js v8.11.3 API docs have an obscure performance warning about unref()ed timers. Check your node version's docs if you care.

Timeout control objects


  • With a positive number as sec: Extend the timeout so it triggers in sec seconds from now.
  • sec === true: Extend timeout to now + the default timespan, which usually is the timeoutSec with which prx was created.
  • sec === null: Just discard the timeout timer.


Shorthand for .renew(null).

Info and Stats

Treat these as read-only.

  • .hasTimedOut: (boolean) Whether the timeout has expired.
  • .hadLateCalls: false = origCb has not been notified yet; non-negative integer: late call counter.
  • .startTime: If timestamps were requested, creation time of the TCO.
  • .finishTime: If timestamps were requested, this starts as false, until the first call to prx, which then stores its current time here.

Config options

These should be safe to modify after prx was created:

  • .limitSec: Has no effect on currently active timers but changes the the default timespan for follow-up .renewals.
  • .onLateCall
  • .errFac


see usage.js.




npm i callback-timeout-flexible

DownloadsWeekly Downloads






Unpacked Size

15.1 kB

Total Files


Last publish


  • avatar