Attempt

Retries functions that throw or call back with an error, in crazily customizable ways.

In your project folder, type:

npm install attempt

Whenever you have code that looks like this:

function flakyApiCall(function(err, result) {
    if (err)
        console.err('Flaky API died AGAIN!');
    else
        doSomething(result);
});

Just drop that code in an attempt!

var attempt = require('attempt');
attempt(function() {
	flakyApiCall(this);
},
function(err, result) {
    if (err)
        console.err('Flaky API failed 5 times.');
    else
        doSomething(result);
});

Attempt will re-run your attempted function if it throws an error or if it calls back with a non-empty first argument (following the first-arg-is-an-error standard Node.js convention). The function call looks like this:

attempt(tryFunc, [options], [callback])

tryFunc is called with one argument: attempts. It is the number of times the tryFunc has been run before.

attempt(function(attempts) {
	if (attempts)
		console.log('This is retry #' + attempts);
	else
		console.log('This is the first attempt!');
});

The following options are set per request:

Default: 5. The number of times to retry the tryFunc before giving up and sending the error to the callback.

attempt(function() {
	flakyApiCall(this);
}, { retries: 15 }, function(err, result) {
	if (err)
		console.err('Failed 16 times.');
	else
		doSomething(result);
});

Default: 0. The number of milliseconds to wait between attempts.

attempt(function() {
    flakyApiCall(this);
}, { interval: 5000 }, function(err, result) {
    if (err)
        console.err('5 retries * 5 seconds = 25 seconds of failure.');
    else
        doSomething(result);
});

Default: 1. The factor by which the interval should be multiplied per attempt. If set to 2 with an interval of 5, the first retry will execute after 5 seconds, the second after 10, the third after 20, and so on.

This allows an exponential retry scheme. For a smaller gap between retries, floats like 1.2 can be used to grow the interval at a slower rate.

Default: null. Function to call when the tryFunc fails with an error. The first argument is the error.

attempt(function() { flakyApiCall(this); },
	{ onError: function(err) { console.err(err); } },
	function(err, result) { /* ... */ });

The second argument, if it exists, is a callback function that will need to be called in order for the next attempt to continue. This is useful if you have to do something asynchronous to fix the error.

attempt(function() { flakyApiCall(this); },
	{ onError: function(err, done) {
		log.write(err, done);
	} },
	function(err, result) { /* ... */ });

By default, calling done() will ignore the retry interval. If you still want it to be observed, call done(true).

Default: 0. The number of attempts to fake Attempt into believing were already completed. This is mostly used by Attempt internally, but can be useful for hacking interval times.

Attempt is distributed under the MIT license.

Attempt was created by Tom Frost in 2012. Because webservice APIs be flaky, man.