fetch-retry

What is fetch-retry?

The fetch-retry npm package is an extension of the native fetch API that adds the ability to automatically retry a failed HTTP request. This is particularly useful for dealing with transient network issues or temporary server-side errors. It allows developers to specify the number of retries, the retry delay, and other retry policies.

What are fetch-retry's main functionalities?

Automatic retries for failed requests

This feature allows fetch requests to be automatically retried a specified number of times with a delay between each attempt. The code sample shows how to wrap the native fetch with fetch-retry to make a GET request that retries up to 3 times with a 1-second delay between retries.

fetch = require('fetch-retry')(require('node-fetch'));

fetch('https://api.example.com', {
  retries: 3,
  retryDelay: 1000
}).then(function(response) {
  return response.json();
}).then(function(json) {
  console.log(json);
}).catch(function(error) {
  console.error(error);
});

Customizable retry on function

This feature allows developers to define a custom function to determine whether a request should be retried based on the attempt number, error, and response. The code sample demonstrates a custom retryOn function that retries the request if an error occurs or if the response status code is 500 or greater.

fetch = require('fetch-retry')(require('node-fetch'));

fetch('https://api.example.com', {
  retries: 4,
  retryDelay: 1000,
  retryOn: function(attempt, error, response) {
    if (error !== null || response.status >= 500) {
      return true;
    }
    return false;
  }
}).then(function(response) {
  return response.json();
}).then(function(json) {
  console.log(json);
}).catch(function(error) {
  console.error(error);
});

Other packages similar to fetch-retry

axios-retry

axios-retry is a package that provides similar retry functionality for Axios, a popular HTTP client. It allows for configuring retry conditions, delay strategies, and the number of retries. Unlike fetch-retry, which is built for the fetch API, axios-retry is specifically designed to work with Axios.

got

got is a more comprehensive HTTP request library that includes built-in retry functionality among many other features. It supports retries with a more extensive set of options and strategies compared to fetch-retry. Got is a standalone package, whereas fetch-retry is an extension of the native fetch API.

superagent-retry

superagent-retry extends the superagent library to add retry capabilities. It is similar to fetch-retry in that it adds retry functionality to an existing HTTP request library, but it is designed for superagent instead of fetch.

README

fetch-retry

Adds retry functionality to the Fetch API.

It wraps any fetch API package (eg: isomorphic-fetch, cross-fetch, isomorphic-unfetch, or Node.js native's fetch implementation) and retries requests that fail due to network issues. It can also be configured to retry requests on specific HTTP status codes.

npm package

npm install fetch-retry --save

Example

fetch-retry is used the same way as fetch, but also accepts retries, retryDelay, and retryOn on the options object.

These properties are optional, and unless different defaults have been specified when requiring fetch-retry, these will default to 3 retries, with a 1000ms retry delay, and to only retry on network errors.

const originalFetch = require('isomorphic-fetch');
const fetch = require('fetch-retry')(originalFetch);

// fetch-retry can also wrap Node.js's native fetch API implementation:
const fetch = require('fetch-retry')(global.fetch);

fetch(url, {
    retries: 3,
    retryDelay: 1000
  })
  .then(function(response) {
    return response.json();
  })
  .then(function(json) {
    // do something with the result
    console.log(json);
  });

or passing your own defaults:

const originalFetch = require('isomorphic-fetch');
const fetch = require('fetch-retry')(originalFetch, {
    retries: 5,
    retryDelay: 800
  });

fetch-retry uses promises and requires you to polyfill the Promise API in order to support Internet Explorer.

Example: Exponential backoff

The default behavior of fetch-retry is to wait a fixed amount of time between attempts, but it is also possible to customize this by passing a function as the retryDelay option. The function is supplied three arguments: attempt (starting at 0), error (in case of a network error), and response. It must return a number indicating the delay.

fetch(url, {
    retryDelay: function(attempt, error, response) {
      return Math.pow(2, attempt) * 1000; // 1000, 2000, 4000
    }
  }).then(function(response) {
    return response.json();
  }).then(function(json) {
    // do something with the result
    console.log(json);
  });

Example: Retry on 503 (Service Unavailable)

The default behavior of fetch-retry is to only retry requests on network related issues, but it is also possible to configure it to retry on specific HTTP status codes. This is done by using the retryOn property, which expects an array of HTTP status codes.

fetch(url, {
    retryOn: [503]
  })
  .then(function(response) {
    return response.json();
  })
  .then(function(json) {
    // do something with the result
    console.log(json);
  });

Example: Retry custom behavior

The retryOn option may also be specified as a function, in which case it will be supplied three arguments: attempt (starting at 0), error (in case of a network error), and response. Return a truthy value from this function in order to trigger a retry, any falsy value will result in the call to fetch either resolving (in case the last attempt resulted in a response), or rejecting (in case the last attempt resulted in an error).

fetch(url, {
    retryOn: function(attempt, error, response) {
      // retry on any network error, or 4xx or 5xx status codes
      if (error !== null || response.status >= 400) {
        console.log(`retrying, attempt number ${attempt + 1}`);
        return true;
      }
    })
    .then(function(response) {
      return response.json();
    }).then(function(json) {
      // do something with the result
      console.log(json);
    });

Example: Retry custom behavior with async

The retryOn option may also be used with async and await for calling asyncronous functions:

fetch(url, {
    retryOn: async function(attempt, error, response) {
      if (attempt > 3) return false;

      if (error !== null) {
        var json = await response.json();
        if (json.property !== undefined) {
          return true;
        }
      }
    })
    .then(function(response) {
      return response.json();
    }).then(function(json) {
      // do something with the result
      console.log(json);
    });