Pipe-line

A task assembler, to divide large tasks into independent and testable small task, and pipe them!

Usage

Install Pipe-line.

npm install --save pipe-line

Registering and executing tasks with pipeline.

// Import Pipeline
let Pipeline = require('pipe-line').Pipeline;

let pipe = new Pipeline('myPipe', null);

let something = getValue();

pipe.register((input, next) => { // A custom task with param input and next Function
  // Do something.
  setTimeout(() => {
    if (!something) {
      return next(new Error('Something is undefined'));
    }
    // Pass value to the next task.
    // First param - error
    // Second param - value to be passed to the next task
    return next(null, 10);
  }, 2000);
});

// Use ES5 function, to get a hold of the current task scope.
// 'this' scope will be unavailable when using ES6 arrow function.

// Actions parameter is an object containing exit & next Function.
pipe.register(function(input, next, actions) {
  let _self = this; // Task Scope. 
  
  if (someCondition) {
    return actions.exit(input + 2); // For Graceful pipeline exit.
  }
  
  _self.log('My Log message', 'and more message'); // Triggers the event 'log'
});

// Handling events

// Error event.
// params -> err, and name of the task it failed.
pipe.on('error', (err, taskName) => {
  // Handle stuff
});

// Log event.
pipe.on('log', (message, taskName) => {
  myLogger.info(message, taskName);
});


// Task start event.
// Triggers when a task starts.
pipe.on('task:start', (taskName) => {
  myLogger.info(`${taskName} started...`);
});

// Task Complete event.
// Triggers when a particular task finished executing.
// params -> taskName and ElapsedTime - Time elapsed for the task.
pipe.on('task:complete', (taskName, elapsedTime) => {
  myLogger.info(`${taskName} completed in ${elapsedTime}`);
});

// Done event.
// triggered when the pipeline completes executing all the tasks.
pipe.on('done', (result) => {
  // Result of the pipeline.
});

// Can register multiple tasks, each task's output will be input for the next task.
// Registering tasks can be chained.
// pipe.register(fn).register(fn).register(fn) ....

// Execute the pipeline containing the registered tasks, with an initial parameter.
// it returns a promise.
let pipePromise = pipe.execute(10); // this will be passed on to (input, next) => console.log(input); // 10;

// Any error thrown inside the task handler, will be handled in promise's catch block 
pipePromise.then((result) => console.log(result)).catch(console.error);

Using a dispatcher

A dispatcher is basically a conditional pipeline runner, Dispatcher takes in array of Pipelines as constructor param, and a dispatch function takes first param as a predicate and second param as the initial input just like Pipeline.execute(input)

  // Import dispatcher.
  const Dispatcher = require('pipe-line').Dispatcher;
  
  // Import pipeline
  const Pipeline = require('pipe-line').Pipeline;
  
  // Create pipelines that executes different tasks.
  let pipeOne = new Pipeline('pipeOne');
  let pipeTwo = new Pipeline('pipeTwo');
  
  // Load the pipelines into the dispatcher in the form of an array.
  let dispatcher = new Dispatcher([pipeOne, pipeTwo]);
  
  
  // First param - a predicate function that returns the name of a pipeline.
  // Second param - the initial input value, that needs to be passed onto the selected pipeline.
  // It also executes the pipeline and returns a promise with the result of the pipeline.
  // Returns a promise.
  dispatcher.dispatch(function() {
    if (someCondition) {
      return 'pipeOne'; // Pipeline name
    } else {
      return 'pipeTwo';
    } 
  }, 10).then((result) => {
    console.log(result);
  });;