#Guarantee

A failsafe wrapper for asynchronous functions.

Installation

$ npm install guarantee

Usage

var guarantee = require('guarantee');

// an async function ( for example: using unstable remote resources sensible to Operational Errors)
var unstableAsyncFunction = function() { return Promise.resolve('I am not stable'); }

// create a `guaranteed` function from the original function
var guaranteed = guarantee(unstableAsyncFunction, { cacheFor: 5000, maxDuration: 500, fallbackAfter: 200 })

// using the guaranteed wrapper you can trust that:
//  1 - "unstableAsyncFunction" will never be called more than once every 5 seconds
//  2 - the "guaranteed" function will never take more than 200ms (otherwise a fallback value will be sent)
//  3 - In case of errors the previously resolved value will be sent.
guaranteed().then(function(val) { console.log(val); })

API

var guaranteed = guarantee(

  // can be a Promise factory or a callback accepting function
  // ex: function asyncFunction(cb) { setTimeout(function() { cb(null, 'Hello'); }) }
  function() { return Promise.resolve('Hello'); },

  // options [Optional]
  {
    // How long can the task be running  (default = 4000)
    maxDuration: 500 // [Optional] <Number> (ms)

    // how long a consumer should try to run the task
    // before beeing sent a fallback value (from the previous run)
    // has no effect if no fallback value
    fallbackAfter: 200, // [Optional] <Number> (ms)

    // Initial fallback value
    fallback: 'initial fallback value', // [Optional] <Any>

    // How long to cache the value for (default = 0)
    cacheFor: 3000, // [Optional] <Number> (ms)

    // logging
    logger: true // [Optional] <Boolean> uses console.log if true (default = false)
    logger: 'task-name' // [Optional] <Boolean> uses console.log and prefix with the value. ex: console.log('task-name' + ...)
    logger: customLogger // [Optional] <Function> uses passed in customLogger instead of console.log

    // Hooks

    // Called when the task is actualy called
    onRun: function() {} // [Optional] <Function>

    // Called when the task successfuly finished running
    // info.duration => How long it took (ms)
    onCompleted: function(info) {} // [Optional] <Function>

    // Called when the task throw an exception
    // info.error => error object,
    // info.hasFallback => wheter or not a fallback value was sent
    // info.duration => How long it took
    onError: function(info) {} // [Optional] <Function>

    // Called when explicitly falling back after options.fallbackAfter
    // info.duration => How long it took
    onFallback: function(info) {} // [Optional] <Function>

    // Called when sending data from the cache during options.cacheFor
    // info.duration => How long it took
    onCache: function(info) {} // [Optional] <Function>

    // Called when a new consumer is joining a pending task
    onMerge: function() {} // [Optional] <Function>


  }

)

Licence

The MIT License (MIT)

Copyright (c) 2015 Romaric Laurent

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.