1.3.3-hola.1 • Public • Published

Lolex Build Status

JavaScript implementation of the timer APIs; setTimeout, clearTimeout, setImmediate, clearImmediate, setInterval, clearInterval, and requestAnimationFrame, along with a clock instance that controls the flow of time. Lolex also provides a Date implementation that gets its time from the clock.

Lolex can be used to simulate passing time in automated tests and other situations where you want the scheduling semantics, but don't want to actually wait. Lolex is extracted from Sinon.JS.


Lolex can be installed using npm:

npm install lolex

If you want to use Lolex in a browser, you have a few options. Releases are hosted on the sinonjs.org website. You can also get the node module and build a file for the browser using browserify:

npm install lolex
npm install browserify # If you don't already have it globally installed
browserify node_modules/lolex/lolex.js


To use lolex, create a new clock, schedule events on it using the timer functions and pass time using the tick method.

// In the browser distribution, a global `lolex` is already available
var lolex = require("lolex");
var clock = lolex.createClock();

clock.setTimeout(function () {
    console.log("The poblano is a mild chili pepper originating in the state of Puebla, Mexico.");
}, 15);

// ...


Upon executing the last line, an interesting fact about the Poblano will be printed synchronously to the screen. If you want to simulate asynchronous behavior, you have to use your imagination when calling the various functions.

Faking the native timers

When using lolex to test timers, you will most likely want to replace the native timers such that calling setTimeout actually schedules a callback with your clock instance, not the browser's internals.

To hijack timers in another context, use the install method. You can then call uninstall later to restore things as they were again.

var lolex = require("lolex");
var clock = lolex.install(window);

window.setTimeout(fn, 15); // Schedules with clock.setTimeout


// window.setTimeout is restored to the native implementation

In 90% av the times, you want to install the timers onto the global object. Calling install with no arguments achieves this:

var clock = lolex.install();

// Equivalent to
// var clock = lolex.install(typeof global !== "undefined" ? global : window);

API Reference

var clock = lolex.createClock([now])

var clock = lolex.install([context[, now[, toFake]]])

var clock = lolex.install([now[, toFake]])

var id = clock.setTimeout(callback, timeout)


var id = clock.setInterval(callback, timeout)


var id = clock.setImmediate(callback)




This simulates a user changing the system clock while your program is running. It affects the current time but it does not in itself cause e.g. timers to fire; they will fire exactly as they would have done without the call to setSystemTime().



Running tests

Lolex has a comprehensive test suite. If you're thinking of contributing bug fixes or suggest new features, you need to make sure you have not broken any tests. You are also expected to add tests for any new behavior.

On node:

npm test

Or, if you prefer slightly less verbose output:

mocha ./test/lolex-test.js

In the browser


BSD 3-clause "New" or "Revised" License (see LICENSE file)




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npm i @hola.org/lolex

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