Promise Flow Extensions

This are simple extensions to make handling some common promise flows a bit more simple.

Instalation:

$ npm install --save promise-flow-extensions

Usage

The library can be used in three ways

Directly accessing the helper methods:

const promiseFlowExt = require('promise-flow-extensions');
 
promiseFlowExt.if(Promise.resolve(2), {condition: v => v > 1, true: v => v - 1})
  .then(console.log); // 1

Important! when using functions this way, the first parameter is always the promise

Extending a specific promise:

const promiseFlowExt = require('promise-flow-extensions');
 
const eventually2 = Promise.resolve(2);
promiseFlowExt.extend(eventually2);
eventually2.if({condition: v => v > 1, true: v => v - 1})
  .then(console.log); // 1

Extending all promises

const promiseFlowExt = require('promise-flow-extensions');
promiseFlowExt.extend(Promise.prototype);
 
const eventually2 = Promise.resolve(2);
eventually2.if({condition: v => v > 1, true: v => v - 1})
  .then(console.log); // 1

Removing the extensions

You can reset an extended object (i.e. remove all the added methods) by running

const promiseFlowExt = require('promise-flow-extensions');
promiseFlowExt.extend(Promise.prototype);
promiseFlowExt.reset(Promise.prototype);
 
const promise = Promise.resolve(1);
promise.rethrow(() => null) // promise.rethrow is not a function
  .then(console.log);

Methods

All methods can be called using the 3 options shown above, we'll assume we have extended all promises for all examples.

rethrow(function)

Catches and exception and executes the passed function. Then it rethrows the exception received. The function receives the thrown error as an argument.

Promise.reject(new Error('test'))
  .rethrow(e => console.log(e.message)) // test
  .then(v => 'this is never called')
  .catch(e => /* actually handle the error */);

if(trueFn | {condition, true, false})

Executes the passed function if the promise is true. Instead of a function you can provide an object, specify up to 3 values, if any of those values isn't specified, the default is the identity function, i.e. v => v

• condition: a function that will be used to evaluate if the promise result is true/false
• true: The function that will be executed when the condition is true
• false: The function that will be executed when the condition is false

Promise.resolve('test')
  .if({
    condition: v => v === 'test',
    true: v => v + ' ok!',
    false: v => 'this is never called'
  }) // 'test ok!'
  .then(console.log); // 'test ok!'

retry(function, [condition, [options]])

Executes the passed function. It will check the result (or the result of calling condition with the result if a condition is provided). If it's false it will retry the function options.retries times (default: 1), waiting options.interval milliseconds (default 1000) between retries.

option.interval is a function, that is called each time with the number of retries remaining.

If retries run out it will reject the promise with an exception.

Promise.resolve('http://example.org/my-simple-service')
  .retry(u => callService(u), r => r.body === 'ok', {
    retries: 10,
    interval: retries => (10 - retries) * 1000
  })
  .catch(e => {body: 'failed'})
  .then(console.log); // something like {body: ok} ok {body: 'failed'}