ember-pipeline

Railway oriented programming in Ember. To install:

ember install ember-pipeline

Philosophy

ember-pipeline allows you to compose a pipeline of (promise aware) methods on an object using "railway oriented programming". That is, if any of the methods in the pipeline returns a CANCEL token, the entire pipeline exits and can be optionally handled by another method. If the host Ember.Object is destroyed, the pipeline is aborted as well.

For example:

import Ember from 'ember';
import { pipeline, step, CANCEL } from 'ember-pipeline';

const { computed, get } = Ember;

export default Component.extend({
  fetchStoreLocations: computed(function() {
    return pipeline(this, [
      step('requestGeolocation'),
      step('fetchStoresInProximity'),
      step('sortStoresByDistance'),
      step('alwaysCancels')
    ]).onCancel((cancellation) => this.handleCancel(cancellation));
  }),

  requestGeolocation() { /* ... */ },
  fetchStoresInProximity() { /* ... */ },
  sortStoresByDistance() { /* ... */ },

  alwaysCancels() {
    return CANCEL();
  },

  handleCancel(cancellation) {
    switch (cancellation.fnName) {
      case 'requestGeolocation':
        // show error message saying you didn't allow us to use geo api
        break;
      case 'fetchStoresInProximity':
        // no stores around you, sorry!
        break;
      case 'sortStoresByDistance':
        // we used bubble sort
        break;
      default:
        // no cancel handler
        console.log(`last value: ${cancellation.result}, reason: ${cancellation.reason}`);
        break;
    }
  }),

  actions: {
    fetchStoreLocations(...args) {
      return get(this, 'fetchStoreLocations').perform(...args);
    }
  }
});

Usage

First, create a pipeline using pipeline and step. You can also define a cancel handler:

return pipeline(this, [
  step('step1'),
  step('step2'),
  step('step3')
]).onCancel((cancellation) => this.handleCancel(cancellation));

If using inside of an Ember.Object, you could make this a computed property:

export default Component.extend({
  myPipeline: computed(function() {
    return pipeline(this, [
      step('step1'),
      step('step2'),
      step('step3')
    ]).onCancel((cancellation) => this.handleCancel(cancellation));
  })
});

step receives either a method name as a string, or a function:

[step('step1'), step(x => x * x)];

In a step function, return CANCEL() to abort the pipeline:

{
  step1() {
    return CANCEL('optional reason, can be any type');
  }
}

Then, to run the pipeline, get the reference to it and perform it:

get(this, 'myPipeline').perform(...args);
pipelineInstance.perform(...args);

You can compose new pipelines at runtime. For example:

export default Component.extend({
  makePipeline(steps) {
    return pipeline(this, steps)
      .onCancel((cancellation) => this.handleCancel(cancellation));
  },

  // ...

  actions: {
    normal(...args) {
      return this.makePipeline([step('step1'), step('step2')]).perform(...args);
    },

    reverse(...args) {
      return this.makePipeline([step('step2'), step('step1')]).perform(...args);
    }
  }
});

After a pipeline has been performed, you can get derived state:

get(this, 'myPipeline').perform(1, 2, 3);
get(this, 'myPipeline.successfulSteps.length'); // 2
get(this, 'myPipeline.cancelledSteps.length'); // 1
get(this, 'myPipeline.successfulSteps'); // array of successful Steps
get(this, 'myPipeline.cancelledSteps'); // array of cancelled Steps

API

Because features are still in flux, detailed API docs are coming soon!

Roadmap

Support ember-concurrency tasks

Installation

git clone <repository-url> this repository
cd ember-pipeline
npm install
bower install

Running

ember serve
Visit your app at http://localhost:4200.

Running Tests

npm test (Runs ember try:each to test your addon against multiple Ember versions)
ember test
ember test --server

Building

ember build

For more information on using ember-cli, visit https://ember-cli.com/.

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