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All problems in computer science can be solved by another level of indirection

TIMER-SHIM is a simple wrapper around standard timer functions adding the ability to mock / stub / test timing functions with ease.

If you have trouble getting mocha and sinon fake timers to behave, or you have trouble testing code that depends on setTimeout and/or setInterval you will find this simple comes in quite handy.

Additionally, TIMER-SHIM also provides a few niceties over standard timer functions, including:

  • Call with timeout number before the function (or vice versa - doesn't matter.)
  • Shorter and simpler aliases without any magic or prototype infection.
  • Protect against NaN and non-function values to save you debugging time.

And best of all:

  • Provides pause(), resume() and wind() so you can test your timing functionality directly in a sane way.

At its core, the shim simply delegates calls to setTimeout/setInterval internally but by calling those function via TIMER-SHIM you can more easily test your time-dependent code.

There is a little caveat though, as I try not to pollute your global namespace in that you must update all your setTimeout and setInterval to use TIMER-SHIM's provided functions instead to be able to use the time simulation functions.

Internally a node-linkedlist is used to track scheduled tasks with very basic adaptive cleanup. From a set of benchmarks I have ran, using TIMER-SHIM vs setTimeout adds no more than 100ms overhead for 100,000 tasks on a decent MBA. This overhead will be completly togglable in the future so you can have shims for tests and zero overhead for production.


$ npm install timer-shim --save


var timer = require('timer-shim')
  , count = 0
  , handle = null;
timer.timeout(50, function() { console.log('hello!'); });
handle = timer.interval(100, function() {
  if (count === 10) timer.clear(handle);

See example/code.js and example/test.js for an example on how to write code / test the code.


Internal class for handling timers. Instances exports the same API as the module itself. You can create multiple instances of this class if you need to pause(), resume() and wind() only a certain set of functions while leaving other set of functions still working normally.

Clears the timeout handle given. Only works with TIMER-SHIM's provided handles. Does not works with handles returned from native setTimeout or setInterval.

Clears all registered timeout handles. Effectively cancels all scheduled timeout and intervals. Useful for reseting the timer in tests.

Schedules a function to run after the specified timeout. Returns a TIMER-SHIM handle.

Schedules a function to run repeatedly every set interval. Returns a TIMER-SHIM handle.

Pauses all timing functions that has not yet run and all functions that may be scheduled in the future.

Resumes all scheduled function as though the time hasn't flickered.

timer.wind( time )
Only works when paused. Winds the internal clock by the specified time (in ms) running anything that is scheduled to be run in that amount of time. resume()-ing after this point will execute any scheduled functions as though time has passed (i.e. shorter timeout, shorter first invocation of interval function)

Calls unref() if inside node.js environment. Effectively prevents all timers set so far to keep the process alive if they are the only thing waiting to run inside the event loop. Useful for cleaning up after timer tests.

Calls ref() if inside node.js environment. Reverses the effect of unref().


Both timer.timeout and timer.interval can be called in either of the following ways:

timer.timeout(100, function() { }); // both works 
timer.timeout(function() { }, 100);
timer.interval(100, function() { }); // also works 
timer.interval(function() { }, 100);


All timers are ref()-ed by default. See node.js timers doc for more information about ref() and unref(). For convenience timer-shim provides a top-level unref() method to unref() on all timers.


Test with:

make test

Compiles with:

$ make lib/timer-shim.js


  • Ability to infect global setTimeout/setInterval and route it to call the shim functions instead.
  • Ability to un-shim the the shims and send calls directly to setTimeout/setInterval virtually removing any perf and mem impact (i.e. in production.)
  • Performance optimizations.
  • nextTick support?




Just open a GitHub issue or ping me @chakrit on Twitter.