Pipeline pattern implementation with the support for sync and async stages
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README.md

pipeline-js

Build Status Package Version

Hassle free pipeline pattern implementation with the support for sync and async stages

Introduction

Pipeline JS allows you to implement the pipeline pattern while creating reusable pipelines in your Javascript applications. You can create pipelines consisting of one or more stages once and then process them using different payloads. Pipeline processing is initiated by some payload and this payload will be passed from stage to stage in order to complete the required process.

General Pipeline Example

To demonstrate it using an example, consider a request made to access user by id; the pipeline may consist of stages including getUserById, transformUser, convertToJson and return. And for each next stage, the input comes from the last stage i.e.

->(User ID)>>getUserById()
    ->(User Detail)>>transformUser()
          ->(Transformed Detail)>>convertToJson()
                  ->(User Detail.json)>>return

Sample Programmatic implementation

While using Pipeline JS, it can be written programmatically as

// First syntax
var userPipeline = new Pipeline([
    getUserById,
    transformUser,
    convertToJson
]);

// Alternatively, you may write the same using the pipe method
var userPipeline = (new Pipeline()).pipe(getUserById)
                                   .pipe(transformUser)
                                   .pipe(convertToJson);

// Then this pipeline can be used with any payload i.e.
var userJson = userPipeline.process(10);  // JSON detail for the user with ID 10
var userJson = userPipeline.process(23);  // JSON detail for the user with ID 23

Where stages shown above can be anything invokable. The sample implementation for the stages may be something like below

// For example, methods from some objects
var getUserById   = UserModel.getUserById,
    transformUser = Transformers.transformUser,
    convertToJson = Utility.convertToJson;

// Or functions
var getUserById = function (userId) {
    //..
    return promise;
};

var transformUser = function (userDetail) {
    // ..
    return transformedObject;
};

var convertToJson = function(userDetail) {
    // ..
    return jsonString;
};

Using pipeline will not only allow constructing reusable pipelines but also result in comparatively cleaner and readable code i.e. consider the following example

  var output = JSON.stringify(transformFilters(getSelectedFilters()));

  // It can be transformed to
  var pipeline = new Pipeline([
    getSelectedFilters,
    transformFilters,
    JSON.stringify
  ]);

  // Or maybe use the alternate syntax
  var pipeline = (new Pipeline()).pipe(getSelectedFilters)
                                 .pipe(transformFilters)
                                 .pipe(JSON.stringify);

  // Get the output by processing the pipeline 
  var output = pipeline.process();

Installation

Run the below command to install using NPM

npm install --save pipeline-js

Usage

Operations in a pipeline i.e. stages can be anything that is callable i.e. closures and anything that's invokable is good.

In order to create a pipeline, you can either pass the stages as an array parameter to constructor

var pipeline = require('pipeline-js');

// Creating pipeline using constructor parameterå
var pipeline = new Pipeline([
  invokableStage1,
  invokableStage2,
  invokableStage3
]);

// Process pipeline with payload1
var output1 = pipeline.process(payload1);
var output2 = pipeline.process(payload2);

Or you can create a pipeline object and call the pipe method on it to successively add the invokable stages

var pipeline = require('pipeline-js');

// Creating pipeline using pipe method
var pipeline = (new Pipeline()).pipe(invokableStage1)
                               .pipe(invokableStage2)
                               .pipe(invokableStage3

// Process pipeline with payload1
var output1 = pipeline.process(payload1);
var output2 = pipeline.process(payload2);

Sync/Async Usage

The only difference between the synchronous usage and asynchronous usage is how the output is handled. For both types of usages, pipelines are created the same way. The difference is when you call the process() method, if the pipeline has all the stages returning concrete output the process method returns concrete value, however if any of the stages returns a promise then the process method returns promise and you will have to use .then() to get the output.

Examples for both the sync and async usage are given below

Sync Example

How to use when all the stages return concrete values?

If none of the stages return promise then process(payload) will return concrete value

var addOne = function (x) {
  return x + 1;
};

var square = function (x) {
  return x * x;
};

var minusTwo = function (x) {
  return x - 2;
};

// Without pipeline
// - Not reusable
// - Not that clean
var output1 = minusTwo(square(addOne(10)));
var output2 = minusTwo(square(addOne(10)));

// With Pipeline
// Reusable with different payload
// Cleaner
var someFormula = new Pipeline([
  addOne,
  square,
  minusTwo
]);

var result = someFormula.process(10);   // 10 + 1  => 11
                                        // 11 * 11 => 121
                                        // 121 - 2 => 119
console.log(result);  // (int) 119

var result = someFormula.process(20);   // 20 + 1  => 21
                                        // 21 * 21 => 441
                                        // 441 - 2 => 339
console.log(result); // (int) 339

Or maybe you can write the same example as

var someFormula = (new Pipeline()).pipe(addOne)
                                  .pipe(square)
                                  .pipe(minusTwo);

var output1 = someFormula.process(20);
var output2 = someFormula.process(20);

Async Example

How to use when one or all of the stages return promise?

If any single of the stages returns a promise, process(payload) will return a promise

var Pipeline = require('pipeline-js');

// Gets the user by ID and returns promise
var getUserById = function (userId) {
  var q = q.defer();
  // ..
  return q.promise;
};

// Transforms the user
var transformUser = function (userDetai) {
  return {
    name: userDetail.name,
    email: userDetail.email,
    password: '*****'
  };
};

// Converts to JSON
var createJson = function (object) {
  return JSON.stringify(object);
};

var pipeline = new Pipeline([
    getUserById,    // Returns promise
    transformUser,
    createJson
]);

// process() will return promise; since one of the stages returns a promise
var output = pipeline.process(142)
                     .then(function(userJson){
                        console.log(userJson);    // (string) {"name": "John Doe", "email": "johndoe@gmail.com", "password": "****"}
                     })
                     .catch(function(error) {
                        console.log(error);
                     });

var output = pipeline.process(263)  // promise will be returned
                     .then(function(userJson){
                        console.log(userJson);    // (string) {"name": "Jane Doe", "email": "janedoe@gmail.com", "password": "****"}
                     })
                     .catch(function(error) {
                        console.log(error);
                     });

Altneratively,

// Same pipeline using `pipe` method
var pipeline = (new Pipeline()).pipe(getUserById)     // Returns promise
                               .pipe(transformUser)
                               .pipe(createJson);

var output = pipeline.process(142)  // promise will be returned; since one of the stages returns a promise
                     .then(function(userJson){
                        console.log(userJson);    // (string) {"name": "John Doe", "email": "johndoe@gmail.com", "password": "****"}
                     })
                     .catch(function(error) {
                        console.log(error);
                     });

Sidenote

You may also want to check this pipeline proposal

Contribution

Feel free to fork, extend, create issues, create PRs or spread the word.

License

MIT © Kamran Ahmed