Huge News!Announcing our $40M Series B led by Abstract Ventures.Learn More
Socket
Sign inDemoInstall
Socket

polly-js

Package Overview
Dependencies
Maintainers
1
Versions
31
Alerts
File Explorer

Advanced tools

Socket logo

Install Socket

Detect and block malicious and high-risk dependencies

Install

polly-js

Transient exception handling

  • 1.5.0
  • Source
  • npm
  • Socket score

Version published
Weekly downloads
33K
increased by6.67%
Maintainers
1
Weekly downloads
 
Created
Source

polly-js

Greenkeeper badge Transient exception handling for JavaScript made easy.

npm version Bower npm downloads Dependency Status Build Status codecov.io

Polly-js is a library to help developers recover from transient errors using policies like retry or wait and retry.

Polly-js

The typical use case for polly-js are retrying actions after they fail. These actions often include some form of IO which can fail. Examples of these IO actions are AJAX requests to other services, file operations on disk or interacting with a database. All these actions share the characteristics that they can occasionally fail because of circumstances outside of the control of your application like the network connection might be briefly unavailable or the file might be in use by another process. When any of these actions fail there is a change that just retrying the same action, possibly after a short delay, will work. Polly-js makes these retry actions easy to code.

Detecting failures

Depending on the function being executed different ways of detecting failure are used.

When you call polly().execute(<your function>) the code assumes that your code failed and needs to be retried when your function throws an Error.

When you call polly().executeForPromise(<your function>) the code assumes that your code failed and needs to be retried when your function returns a Promise that is rejected.

When you call polly().executeForNode(<your function that accepts a callback>) the code assumes that your code failed and needs to be retried when your function calls the callback with a first non null parameter indicating an error.

Deciding what to do on failure

Whenever a failure is detected Polly-js will try attempt to retry your action.

You get to control how a failure is retried by calling either polly().retry() or polly().waitAndRetry(). Both will retry the failing action but the polly().waitAndRetry() option adds a small delay before retrying. In general polly().waitAndRetry() is probably the more appropriate policy to use as retrying without apause could cause a lot requests. By default both will retry once where polly().waitAndRetry() waits 100 ms before retrying. With either function you can specify a number of retries to attempt on repeated failures. With polly().waitAndRetry() it will double the time between each try. If you want to control the exact delays you can also specify and array with the individual delay values so polly().waitAndRetry(5) is equivalent to polly().waitAndRetry([100, 200, 400, 800, 1600]).

##Deciding what failures to retry Using polly().handle(<function>) you can decide if you want to retry a specific failure. For example you might want to retry an AJAX request returning a 404 response code but not one resulting in a 500 response code. The callback function specified in polly().handle() is called with watever error was received so you can use any property from there and you return true if you want to retry the action or false to stop retrying.

Usage

Try to load the Google home page and retry twice if it fails.

polly()
    .retry(2)
    .executeForPromise(function () {
        return requestPromise('http://www.google.com');
    })
    .then(function(result) {
        console.log(result)
    }, function(err) {
        console.error('Failed trying three times', err)
    });

Try to read a file from disk and retry twice if this fails.

polly()
    .retry(2)
    .executeForNode(function (cb) {
        fs.readFile(path.join(__dirname, './hello.txt'), cb);
    }, function (err, data) {
        if (err) {
            console.error('Failed trying three times', err)
        } else {
            console.log(data)
        }
    });

Only retry 'no such file or directory' errors. Wait 100 ms before retrying.

polly()
    .handle(function(err) {
        return err.code === 'ENOENT';
    })
    .waitAndRetry()
    .executeForNode(function (cb) {
        fs.readFile(path.join(__dirname, './not-there.txt'), cb);
    }, function (err, data) {
        if (err) {
            console.error('Failed trying twice with a 100ms delay', err)
        } else {
            console.log(data)
        }
    });

Acknowledgements

The library is based on the Polly NuGet package by Michael Wolfenden

Keywords

FAQs

Package last updated on 29 Aug 2018

Did you know?

Socket

Socket for GitHub automatically highlights issues in each pull request and monitors the health of all your open source dependencies. Discover the contents of your packages and block harmful activity before you install or update your dependencies.

Install

Related posts

SocketSocket SOC 2 Logo

Product

  • Package Alerts
  • Integrations
  • Docs
  • Pricing
  • FAQ
  • Roadmap
  • Changelog

Packages

npm

Stay in touch

Get open source security insights delivered straight into your inbox.


  • Terms
  • Privacy
  • Security

Made with ⚡️ by Socket Inc