Because everyone loves a tryer! Conditional and repeated function invocation for node and browser.
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Sometimes, you want to defer calling a function until a certain pre-requisite condition is met. Other times, you want to call a function repeatedly until some post-requisite condition is satisfied. Occasionally, you might even want to do both for the same function.
To save you writing
explicit conditions
and loops
on each of those occasions,
tryer
implements
a predicate-based approach
that hides the cruft
behind a simple,
functional interface.
Additionally, it allows you to easily specify retry intervals and limits, so that your code doesn't hog the CPU. It also supports exponential backoff of retry intervals, which can be useful when handling indefinite error states such as network failure.
5.6 kb unminified with comments, 1.1 kb minified, 0.5 kb minified + gzipped.
Via npm:
npm i tryer --save
Or if you just want the git repo:
git clone git@github.com:philbooth/tryer.git
If you are running in
Node.js
or another CommonJS-style
environment,
you can require
tryer like so:
const tryer = require('tryer');
It also the supports the AMD-style format preferred by Require.js.
If you are
including tryer
with an HTML <script>
tag,
or neither of the above environments
are detected,
it will be exported globally as tryer
.
tryer
is a function
that can be invoked to
call other functions
conditionally and repeatedly,
without the need for
explicit if
statements
or loops in your own code.
tryer
takes one argument,
an options object
that supports
the following properties:
-
action
: The function that you want to invoke. Ifaction
returns a promise, iterations will not end until the promise is resolved or rejected. Alternatively,action
may take a callback argument,done
, to signal that it is asynchronous. In that case, you are responsible for callingdone
when the action is finished. Ifaction
is not set, it defaults to an empty function. -
when
: A predicate that tests the pre-condition for invokingaction
. Untilwhen
returns true (or a truthy value),action
will not be called. Defaults to a function that immediately returnstrue
. -
until
: A predicate that tests the post-condition for invokingaction
. Afteruntil
returns true (or a truthy value),action
will no longer be called. Defaults to a function that immediately returnstrue
. -
fail
: The error handler. A function that will be called iflimit
falsey values are returned bywhen
oruntil
. Defaults to an empty function. -
pass
: Success handler. A function that will be called afteruntil
has returned truthily. Defaults to an empty function. -
limit
: Failure limit, representing the maximum number of falsey returns fromwhen
oruntil
that will be permitted before invocation is deemed to have failed. A negative number indicates that the attempt should never fail, instead continuing for as long aswhen
anduntil
have returned truthy values. Defaults to-1
. -
interval
: The retry interval, in milliseconds. A negative number indicates that each subsequent retry should wait for twice the interval from the preceding iteration (i.e. exponential backoff). The default value is-1000
, signifying that the initial retry interval should be one second and that each subsequent attempt should wait for double the length of the previous interval.
// Attempt to insert a database record, waiting until `db.isConnected`
// before doing so. The retry interval is 1 second on each iteration
// and the call will fail after 10 attempts.
tryer({
action: () => db.insert(record),
when: () => db.isConnected,
interval: 1000,
limit: 10,
fail () {
log.error('No database connection, terminating.');
process.exit(1);
}
});
// Attempt to send an email message, optionally retrying with
// exponential backoff starting at 1 second. Continue to make
// attempts indefinitely until the call succeeds.
let sent = false;
tryer({
action (done) {
smtp.send(email, error => {
if (! error) {
sent = true;
}
done();
});
},
until: () => sent,
interval: -1000,
limit: -1
});
// Poll a device at 30-second intervals, continuing indefinitely.
tryer({
action: () => device.poll().then(response => handle(response)),
interval: 30000,
limit: -1
});
The dev environment relies on
Chai,
JSHint,
Mocha,
please-release-me,
spooks.js and
UglifyJS.
The source code is in
src/tryer.js
and the unit tests are in
test/unit.js
.
To install the dependencies:
npm i
To run the tests:
npm t
To lint the code:
npm run lint
To regenerate the minified lib:
npm run minify