Modern version of setInterval for promises and async functions available in Node.js and browsers.
npm install set-interval-asyncsetIntervalAsyncModern version of setInterval for promises and async functions available in Node.js and browsers.
setIntervalAsync works both on Node.js and in the browser, providing the same
familiar interface as setInterval for asynchronous functions, while preventing
multiple executions from overlapping in time.
First, install setIntervalAsync using npm or yarn:
``bashUsing npm:
npm install set-interval-async
Now, you can require
in CommonJS:`javascript
const { setIntervalAsync, clearIntervalAsync } = require('set-interval-async');
`Or else, you can use ES6 modules syntax:
javascript
import { setIntervalAsync, clearIntervalAsync } from 'set-interval-async';
`Browser
In the browser, you can add a script tag in your HTML:
html
`After the script is loaded, a variable called
will be defined in the global context. From there you can retrieve the setIntervalAsync and clearIntervalAsync functions.`javascript
var setIntervalAsync = SetIntervalAsync.setIntervalAsync;
var clearIntervalAsync = SetIntervalAsync.clearIntervalAsync;
`Usage
In the most basic scenario, you can use
the same way you would use vanilla setInterval. For example, the following code will print 'Hello' to the console once every second.`javascript
const { setIntervalAsync, clearIntervalAsync } = require('set-interval-async');setIntervalAsync(() => {
console.log('Hello')
}, 1000);
`However, you can also provide an async function (or a function returning a promise), which has the added nicety that now you can wait until the cycle is fully stopped before moving on by using
.`javascript
const { setIntervalAsync, clearIntervalAsync } = require('set-interval-async');const timer = setIntervalAsync(async () => {
console.log('Hello')
await doSomeWork()
console.log('Bye')
}, 1000);
// Or equivalently:
const timer = setIntervalAsync(() => {
console.log('Hello')
return doSomeWork().then(
() => console.log('Bye')
)
}, 1000);
// Later:
await clearIntervalAsync(timer);
// At this point, all timers have been cleared, and the last
// execution is guaranteed to have finished as well.
`This is particularly useful when - for example at the end of a unit test - you want to make sure that no asynchronous code continues running by the time your test manager moves on to the next one.
javascript
it('should test something', async () => {
const timer = setIntervalAsync(/ ... /);
// Do some assertions.
await clearIntervalAsync(timer);
// Interval is now fully stopped.
});
`When Should I Use
?Where
setIntervalAsync really shines is in those situations where the given asynchronous function might take longer to compute than the configured interval and, at the same time, is not safe to execute more than once at a time. Using vanilla setInterval will break your code in this scenario, whereas setIntervalAsync guarantees that the function will never execute more than once at the same time.For example, consider the following code:
`javascript
async function processQueue (queue) {
if (queue.length === 0) {
return;
}
let head = queue[0];
await doSomeWork(head);
queue.shift(); // Removes the first element.
}
`The function above should never get called again before the previous execution is completed. Otherwise, the queue's first element will get processed twice, and the second element will be skipped.
However, with
, the following code is perfectly safe:`javascript
setIntervalAsync(processQueue, 1000, queue)
`since
will guarantee that the function is never executed more than once at any given moment.You can choose whether you wish to use the
Dynamic or Fixed strategies, which will either launch every execution as soon as possible or set a fixed delay between the end of one execution and the start of the next one. See Dynamic and Fixed setIntervalAsync for more details.Dynamic and Fixed
setIntervalAsync provides two strategies which can be used to prevent a recurring function from executing more than once at any given moment:- Dynamic: If possible, the given function is called once every
interval milliseconds. If any execution takes longer than the desired interval, the next execution is delayed until the previous one has finished, and called immediately after this condition is reached.
!Dynamic setIntervalAsync diagram.- Fixed: The given function is called repeatedly, guaranteeing a fixed delay of
interval milliseconds between the end of one execution and the start of the following one.
!Fixed setIntervalAsync diagram.You can choose whichever strategy works best for your application. When in doubt, the
Dynamic strategy will likely suffice for most use cases, keeping the interval as close as possible to the desired one. The default strategy is Dynamic.In Node.js
You can require a specific strategy for
setIntervalAsync using CommonJS with the following snippets:`javascript
// Dynamic strategy.
const { setIntervalAsync, clearIntervalAsync } = require('set-interval-async/dynamic');// Fixed strategy.
const { setIntervalAsync, clearIntervalAsync } = require('set-interval-async/fixed');
`Or else, you can use ES6 modules syntax:
javascript
// Dynamic strategy.
import { setIntervalAsync, clearIntervalAsync } from 'set-interval-async/dynamic';// Fixed strategy.
import { setIntervalAsync, clearIntervalAsync } from 'set-interval-async/fixed';
`In the Browser
After the library has been loaded to the page, a variable called
will be defined in the global context. From there you can retrieve the setIntervalAsync from your desired strategy and clearIntervalAsync functions.`javascript
// Dynamic strategy.
var setIntervalAsync = SetIntervalAsync.dynamic.setIntervalAsync;
var clearIntervalAsync = SetIntervalAsync.clearIntervalAsync;// Fixed strategy.
var setIntervalAsync = SetIntervalAsync.fixed.setIntervalAsync;
var clearIntervalAsync = SetIntervalAsync.clearIntervalAsync;
`API
Function
Executes the given
every intervalMs milliseconds, while preventing multiple concurrent executions. The handler will never be executed concurrently more than once in any given moment.setIntervalAsync for more details on which strategies can be used to determine the effective interval between executions when the handler takes longer than the target interval to complete. The default strategy is Dynamic.`typescript
function setIntervalAsync(
handler: SetIntervalAsyncHandler,
intervalMs: number,
...handlerArgs: HandlerArgs
): SetIntervalAsyncTimer;
`Note: when
is less than 1, it will be set to 1. When intervalMs is greater than 2147483647, it will be set to 2147483647. Non-integer values are truncated to an integer.Function
clearIntervalAsyncStops an execution cycle started by
. Any ongoing function executions will run until completion, but all future ones will be cancelled.`typescript
async function clearIntervalAsync(
timer: SetIntervalAsyncTimer
): Promise;
`The promise returned will resolve once the timer has been stopped and the ongoing execution (if available) has been completed. If the last execution ends in a promise rejection, the promise returned by
will reject with the same value.Type
SetIntervalAsyncHandlerSynchronous or asynchronous function that can be passed in as a handler to
.`typescript
type SetIntervalAsyncHandler = (
...handlerArgs: HandlerArgs
) => void | Promise;
`Type
Return type of
. Does not have any observable properties, but must be passed in as an argument to clearIntervalAsync to stop execution.`typescript
type SetIntervalAsyncTimer;
`Avoiding Deadlock When Clearing an Interval
While calling
to stop an interval is perfectly safe in any circumstance, please note that awaiting its result within the async handler itself will lead to undesirable results.For example, the code below leads to a cyclical promise chain that will never be resolved (the
console.log statement is unreachable).`javascript
const timer = setIntervalAsync(async () => {
// ...
if (shouldStop) {
await clearIntervalAsync(timer);
console.log('Stopped!');
}
}, interval);
`This is the case because:
-
will not resolve until the last execution has finished, and
- the last execution will not finish until await clearIntervalAsync(timer) has been resolved.To prevent this cycle, always allow the async handler to complete without awaiting for the interval to be cleared. For example, by removing the
await keyword entirely or by using an immediately-invoked function expression:`javascript
if (shouldStop) {
(async () => {
await clearIntervalAsync(timer);
console.log('Stopped!');
})();
}
`Motivation
If you've ever had to deal with weird, subtle bugs as a consequence of using
[1] on asynchronous functions, or had to manually reimplement setInterval using setTimeout[2] to prevent multiple executions of the same asynchronous function from overlapping, then this library is a drop-in replacement that will solve your issues.setInterval runs a given function repeateadly, once every fixed number of milliseconds. This may cause problems whenever the function takes longer to execute than the given interval, since it will be called again before the first execution has finished. This is often a problem for non-reentrant functions; ie. functions that are not designed to allow multiple executions at the same time.setIntervalAsync is a drop-in replacement of setInterval which shares the same API but is safe to use with non-reentrant, asynchronous functions. [1] https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/setTimeout
[2] https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/setInterval
Contributing
In order to contribute to this project, you will need to first clone the repository:
`bash
git clone https://github.com/ealmansi/set-interval-async.git
`Make sure that Yarn is installed globally on your system,
install all project dependencies, and build the project:
bash
yarn
yarn build
`Now, you can run the tests and make sure that everything is up and running correctly:
bash
yarn test
`If the previous step succeeds, you're ready to start developing on this project.
Pull requests are welcome!
You can verify that your code follows the project's style conventions the with the following command:
bash
yarn lint
``