promise-flow-extensions
v2.0.0
Published
Extends the Promise object with some additional utility functions
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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'}