povtor

Repeat function call depending on the previous call result and specified conditions.

retry({
    action: axios,
    actionParams: [{url: '/api/some/endpoint'}],
    retryAttempts: [2000, 5000],
    retryTest: (response) => response.data.error,
    retryOnError: true
})
.promise.then((response) => console.log(response.data));

Features

• Repeats calling of any function whether it returns a promise or a usual value (action setting).
• Use returned promise to get function's last result or last error when retry process is finished.
• Specify context (actionContext setting) and parameters (actionParams setting) for function call.
• Retry function call when it throws or returns rejected promise (use retryOnError setting) and/or when it returns normal value or fulfilled promise (use retryTest setting).
• Use a function as value for retryOnError/retryTest setting to specify condition when to retry action call.
• Specify quantity and timeouts of retry attempts (use retryAttempts, retryQty and/or retryTimeout settings).
• Limit overall time of process of retry by timeLimit setting.
• Control the process of calls repeating and stop it when it is necessary.
• Access values and errors that are produced by function during the process.
• Does not have dependencies except for ES 2015 Promise API.
• Small size.

Table of contents

• Installation
• Usage
• Examples
• API
• Related projects
• Contributing
• License

Installation ↑

Node

npm install povtor

Bower

bower install povtor

AMD/UMD, <script>

Use dist/povtor.umd.js (minified version).

Usage ↑

ECMAScript 6+

import {retry, getPromiseField} from 'povtor';

Node

const retry = require('povtor').retry;
const getPromiseField = require('povtor').getPromiseField;

AMD/UMD

define(['path/to/dist/povtor.umd.js'], function(povtor) {
    const retry = povtor.retry;
    const getPromiseField = povtor.getPromiseField;
});

Bower, <script>

<!-- Use bower_components/povtor/dist/povtor.umd.js if the library was installed by Bower -->
<script type="text/javascript" src="path/to/dist/povtor.umd.js"></script>
<script type="text/javascript">
    // povtor is available via povtor field of window object
    const retry = povtor.retry;
    const getPromiseField = povtor.getPromiseField;
</script>

Examples ↑

// Request data from API endpoint and repeat request after 3, then 5, then 7 seconds
// when request is not successful, response data has error flag or value of state field is not 3.
let control = retry({
    action: axios,
    actionParams: [{url: '/api/some/endpoint'}],
    retryAttempts: [3000, 5000, 7000],
    retryTest: (response) => response.data.error || response.data.state !== 3,
    retryOnError: true
});

// control.promise will be resolved when a request is completed successfully and retryTest returns false
// or when all repeats will be made.
control.promise.then((response) => console.log(response.data));

getPromiseField(control);   // Get value of control.promise

// Read file contents every second until it contains specific value.
control = retry({
    action: jsonfile.readFileSync,
    actionParams: ['/path/to/data.json', {'throws': false}],
    retryTimeout: 1000,
    retryTest: (data) => ! data || ! data.result
});

// control.promise will be resolved when the file contains specified value.
control.promise.then((data) => console.log(data.result));
...
control.stop();   // Stop repeating of action

See tests for additional examples.

API ↑

retry(settings: RetrySettings): RetryResult

Call specified function and repeat calls depending on settings.

settings: RetrySettings - an object that can contain the following fields:

• action - a function that should be called. Can return a promise or a value.
• actionContext - an object that should be used as this when calling the action function.
• actionParams - an array of parameters that should be passed into the action function.
• delay - an amount of milliseconds before first call of the action function. When the value is not specified or is negative, the action function will be called immediately first time.
• retryAttempts - an array specifying amount and timeouts between repeated calls of the action function. Each item can be a number or a function (see retryTimeout setting for details). Has priority over retryQty and retryTimeout settings.
• retryQty - maximum number of repeated calls of the action function. A negative value means no restriction. Default value is -1.
• retryTimeout - a timeout between repeated calls of the action function, or a function that returns such timeout. A negative or non-number value means the repeat call will be made without delay (this is applied by default). If specified function returns false then retry process will be finished and result promise will be fulfilled or rejected depending on result of the last action's call.
• retryOnError - a boolean value or a function returning boolean value that specifies whether the action function should be called again when the action function throws an error or returned promise is rejected. When not specified the call of the action function will not be repeated on an error.
• retryTest - a boolean value or a function returning boolean value that specifies whether the action function should be called again after a made call. When not specified the action call will not be repeated.
• timeLimit - time in milliseconds specifying how long retry process can last starting from call of retry function.

The only required field is action.

retry function returns RetryResult - an object that can be used to observe and control the process of calls repeating. RetryResult contains the following fields:

• promise - promise that can be used to observe the process and to get the final value of the action function or the last error.
• attempt - number of calls of the action function that have already made.
• error - last error or value of promise rejection.
• isError - whether the last call of the action function is ended with error.
• result - contains result of each call of the action function.
• settings - settings that were passed to retry function.
• startTime - time in milliseconds when retry function was called.
• stop - function that can be used to stop the process of calls repeating. Returns value of promise field.
• stopped - a boolean value that indicates whether the process of calls repeating is stopped.
• value - a value of last successfull call of the action function. When the action function returns a promise, the value will be result of the promise fulfillment.
• valueWait - a boolean value that indicates whether the action function is producing a result. Useful only when the action function returns a promise. Is set to true when the promise is pending.
• wait - a boolean value that indicates waiting of the next call of the action function. Is set to true during a timeout between calls.

getPromiseField(obj)

Return value of promise field of the passed object.

See doc folder for details.

Related projects ↑

• eva
• wrapme

Contributing ↑

In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code.

License ↑

Copyright (c) 2018-2020 Denis Sikuler Licensed under the MIT license.