Flowa

Service level control flow for Node.js

One execution flow that runs mixed sync and async functions that uses either promises or callbacks running in parallel, sequentially or mixed. 🔥 It can't be easier and more readable !

Hint

Check the suggested way to use Flowa with Express.js.

Demo

Table of Contents

• Features
• Introduction
• Installation
• Usage
  • Shorthand Method
  • Mixed Runners Types
  • Promises
  • Sync Tasks
  • Terminating The Flow
  • Jumping Between Tasks
  • Error Handling
  • Factory Method
  • ES6 Coding Style
  • Use It With Express
• Best Practices
• Debugging Mode
• API
  • Flowa(flow[, name])
  • Flowa.create(flow[, name])
  • run(context, options)
• License

Features

• Writing more readable code for complex logic.
• Works with promises or callbacks.
• Works with sync or async tasks.
• Serial or parallel execution.
• No more callback hells.
• Jumping between tasks.
• Proper error handling.
• Timeouts.

Introduction

Each flow is a set of tasks. It starts by a compound task which is basically a task that groups a set of single or other compound tasks. Single tasks are either async or sync functions that are executed and called by passing an object called context to allow sharing data between tasks and an optional callback function for async tasks that use callbacks instead of promises. Each compound task's sub tasks are executed by a runner that can be a serial execution (default type) or a parallel execution.

Installation

npm install --save flowa

Usage

We need to create a new Flowa object with our flow using new Flowa(flow[, name]), Flowa.create(flow[, name]), or just use the Shorthand Method it is much easier and recommended if you are not planning to execute the same flow again and again.

var Flowa = require('flowa');

// Define the flow
var flowa = new Flowa({

  // Runner type
  type: 'serial',

  // A task that uses a callback
  asyncTaskWithCallback: asyncTaskWithCallback,

  // A task that returns a promise
  asyncTaskWithPromise: asyncTaskWithPromise,

  // A sync task
  syncTask: syncTask

});

Then we need to execute the flow.

// To be used to share data between the tasks
var context = {};

// Execute the tasks
flowa.run(context).then(function(result) {

  console.log(result);

}).catch(function(error) {

  console.error(error);
  
});

And don't forget to write the code for your tasks.

// A task that uses a callback
function asyncTaskWithCallback(context, callback) {

  setTimeout(callback.bind(null, null, 'DummyValue1'), 500);

}

// A task that returns a promise
function asyncTaskWithPromise(context) {

  return Promise.resolve('DummyValue2');

}

// A sync task
function syncTask(context) {

  return 'DummyValue3';

}

Just put the 3 blocks of code together in one script and they will run smoothly.

Shorthand Method

Is it possible to create a flow and execute it using a single function .run() that belongs to the Flowa class.

Flowa.run({

  // Runner type
  type: 'serial',

  // Do task1
  task1: task1,

  // Do task2
  task2: task2

}).then(function(result) {

  console.log(result);

}).catch(function(error) {

  console.error(error);
  
});

Mixed Runners Types

There are no limitations about mixing the runners types. Add type to the compound tasks to specify the runner type. But remember, it is not a good idea to make things too complex.

var flowa = new Flowa({

  // Runner type
  type: 'serial',
  
  // Do task1
  task1: task1,

  // Do task2 and task3 in parallel
  group1: {

    // Runner type
    type: 'parallel',

    // Do task2
    task2: task2,

    // Do task3
    task3: task3,

    // Do task4 and task5 in parallel
    group2: {

      // Runner type
      type: 'serial',

      // Do task4
      task4: task4,

      // Do task5
      task5: task5

    }

  },

  // Do task6
  task6: task6

});

Promises

You can return promises from your tasks instead of using callbacks. The callbacks will be called internally.

function task1(context) {

  return new Promise(function(resolve, reject) {

    resolve();

  });

}

Sync Tasks

You can use sync tasks that doesn't return a promise and doesn't take a second callback argument.

function task1(context) {

  // Do something !!

}

Terminating The Flow

You can terminate the flow (skip executing the remaining tasks) by calling the done method.

function task1(context, callback) {

  this.done();
  callback();

}

Jumping Between Tasks

You can jump forward and backward between tasks that belong to the same parent task and the runner type is serial by calling the jump method with the task name as first argument to jump into it after executing the current task completely. You can jump into a compound task too.

function task1(context, callback) {

  this.jump('task6');
  callback();

}

Loop and Retry

Since we have the ability to jump backward and forward, we can implement a task to try something and another task to check the result to decide either to jump back to the previous task or continue.

function task1(context, callback) {

  // We are just generating a random boolean value here
  context.checkSomething = Math.random() >= 0.5;
  callback();

}

/**
 * Task
 * 
 * @param {Object}   context
 * @param {Function} callback
 */
function task2(context, callback) {

  if (context.checkSomething) {
    return callback();
  }

  // Retry
  this.jump('task1');
  callback();
  
}

Error Handling

The thrown errors and the errors passed as a first argument to the callback function can be handled by attaching a .catch() to the returend promise from run() method.

// Using callbacks (Recommended)
function checkUser(context, callback) {
  callback(new Error('User is not found'));
}

// Using the `throw` operator
function checkUser(context, callback) {
  throw new Error('User is not found');
}

Factory Method

Is it possible to create a new Flowa object by calling .create() method instead of using new Flowa.

Flowa.create({

  // Runner type
  type: 'serial',

  // Do task1
  task1: task1,

  // Do task2
  task2: task2

}).run(context).then(function(result) {

  console.log(result);

}).catch(function(error) {

  console.error(error);
  
});

ES6 Coding Style

You can use the shorthand syntax for naming the tasks by their functions names.

var flowa = new Flowa({

  // Runner type
  type: 'serial',
  
  // Shorthand format for task1: task1
  task1,

  // Shorthand format for task2:task2
  task2,

  // Shorthand format for task3:task3
  task3,

  // Shorthand format for task4:task4
  task4,

  // Shorthand format for task5:task5
  task5,

  // Shorthand format for task6:task6
  task6

});

Use It With Express

You can use Flowa to make more readable and maintainable express.js services.

App.js

To initilize your web server and load your services.

Note: No need to change the code, just add more services at the line 16.

var express = require('express');
var Flowa   = require('./index.js');
var app     = express();

/**
 * A mapping between services names and their handlers
 * @type {Object}
 */
var handlers = {};

/**
 * RESTful API services
 * @type {Array}
 */
var services = [
  {name: 'greeting.get', path: '/greeting/:name', method: 'get'}
];

/**
 * Get a function to handle a specific service
 * 
 * @param  {String}   name the name of the service
 * @return {Function}
 */
function getServiceHandler(name) {

  return function(req, res) {

    var handler = handlers[name];
    var context = {req: req, res: res};

    handler.run(context).then(function() {

      res.end();

    }).catch(function(error) {

      if (res.headersSent) {
        return res.end();
      }

      res.status(500).send({
        error: 'Something went wrong !'
      });

      console.error(error);

    });
    
  };

}

// Foreach service, define its route and attach a handler
services.forEach(function(route) {

  handlers[route.name] = new Flowa(require('./' + route.name)),
  app[route.method](route.path, getServiceHandler(route.name));
  
});

app.listen(3000, console.log.bind(null, 'listening ...'));

Greeting.get.js

An example of a service.

/**
 * Generate a greeting message
 * 
 * @author Mohammad Fares <[email protected]>
 */

var counter = 0;

/**
 * Increment the greeting counter
 * 
 * @param {Object} context
 */
function incrementGreetingCounter(context) {

  context.counterValue = ++counter;

}

/**
 * Generate a greeting message
 * 
 * @param {Object} context
 */
function generateGreetingMessage(context) {

  context.res.send({
    message: 'Hello ' + context.req.params.name,
    counter: context.counterValue
  });

}

module.exports = {

  // Runner type
  type: 'serial',

  // Increment the greeting counter
  incrementGreetingCounter: incrementGreetingCounter,

  // Generate a greeting message
  generateGreetingMessage: generateGreetingMessage

};

Best Practices

• Stick with one coding style.
• Define your flow object in a separated object or better in a separated module.
• Add comments for each task to get a quick overview about all the tasks at one place.
• Each single task should do literally only one task.
• Specifiy the runners types.

Debugging Mode

To watch how the tasks being executed in realtime, you can activate the debug logging via the debug option.

flowa.run(context, {debug: true});

API

Note

A new instance from the class Task is created for each execution for each task.

Flowa(flow[, name])

To create Flowa objects.

| Param | Type | Description | |-------|---------------------|--------------------------------| | flow | Object | A compound task | | name | String | A name for the flow (Optional) |

Flowa.create(flow[, name]) ⇒ Flowa

A factory method to create Flowa objects.

Returns: Flowa - a new Flowa object

| Param | Type | Description | |-------|---------------------|--------------------------------| | flow | Object | A compound task | | name | String | A name for the flow (Optional) |

Flowa.run(flow[, context, options]) ⇒ Promise

Create a flow and execute it.

Returns: Promise - resolve with the passed context object

| Param | Type | Description | |---------|---------------------|------------------------------------------------------------| | flow | Object | A compound task | | context | Object | A shared object between the tasks (Optional) (default: {}) | | options | Object | (Optional) |

flowa.run(context, options) ⇒ Promise

Execute the flow. The Flowa object can be defined once and executed as many as you need.

Returns: Promise - resolve with the passed context object

| Param | Type | Description | |---------|---------------------|------------------------------------------------------------| | context | Object | A shared object between the tasks (Optional) (default: {}) | | options | Object | (Optional) |

Options:

• timeout: a timeout for the flow in milliseconds. The promise will be rejected with an error object that has (code: ETIMEDOUT) if the timeout is exeeded (type: Number).
• taskTimeout: a timeout for the single tasks in milliseconds. The promise will be rejected with an error object that has (code: ETIMEDOUT) if the timeout is exeeded (type: Number).
• autoInjectResults: Inject the result of each task into the context automatically (type: Boolean) (default: true).
• debug: log the tasks' names in realtime (type: Boolean) (default: false).
• debugCallback: the debug logging function (type: Boolean) (default: console.log).

task.done()

Skip the remaining tasks. Check Terminating The Flow.

task.jump(taskName)

Jump into another task under the same parent after executing the current task. Check Jumping Between Tasks.

| Param | Type | Description | |----------|---------------------|--------------------------------| | taskName | String | The name of the sibling task |

License

This project is under the MIT license.