flowa
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Service level control flow for Node.js
Check the suggested way to use Flowa with Express.js.
Each flow is a set of tasks. It starts by a compound task which is basically a task that groups a set of single tasks. Single tasks are async functions that are executed and called by passing an object called context to allow sharing data between tasks and a callback function. Each compound task's sub tasks are executed by a runner that can be a serial execution (default type) or a parallel execution.
npm install --save flowa
We need to create a new Flowa object with our flow using new Flowa(flow[, name]) or Flowa.create(flow[, name]).
var Flowa = require('flowa');
// Define the flow
var flowa = new Flowa({
// Runner type
type: 'serial',
// A task that uses a callback
task1: task1,
// A task that returns a promise
task2: task2,
// A sync task
task3: task3
});
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 task1(context, callback) {
context.task1 = 1;
console.log('Executing task 1');
setTimeout(callback, 500);
}
// A task that returns a promise
function task2(context) {
context.task2 = 2;
console.log('Executing task 2');
return new Promise();
}
// A sync task
function task3(context) {
context.task3 = 3;
console.log('Executing task 3');
}
Just put the 3 blocks of code together in one script and they will run smoothly.
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);
});
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
});
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();
});
}
You can use sync tasks that doesn't return a promise and doesn't take a second callback argument. The callbacks will be called internally.
function task1(context) {
// Do something !!
}
You can jump forward and backward between tasks that belong to the same parent task and the runner type is serial by passing the name of the task as the second argument to the callback function or as a resolved value if you use promises instead. You can jump into a compound task too.
function task1(context, callback) {
callback(null, 'task6');
}
Or with promises
function task1(context) {
return new Promise(function(resolve, reject) {
resolve('task6');
});
}
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
callback(null, 'task1');
}
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');
}
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);
});
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
});
You can use Flowa to make more readable and maintainable express.js services.
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 ...'));
An example of a service.
/**
* Generate a greeting message
*
* @author Mohammad Fares <faressoft.com@gmail.com>
*/
var counter = 0;
/**
* Increment the greeting counter
*
* @param {Object} context
* @param {Function} callback
*/
function incrementGreetingCounter(context, callback) {
context.counterValue = ++counter;
callback();
}
/**
* Generate a greeting message
*
* @param {Object} context
* @param {Function} callback
*/
function generateGreetingMessage(context, callback) {
context.res.send({
message: 'Hello ' + context.req.params.name,
counter: context.counterValue
});
callback();
}
module.exports = {
// Runner type
type: 'serial',
// Increment the greeting counter
incrementGreetingCounter: incrementGreetingCounter,
// Generate a greeting message
generateGreetingMessage: generateGreetingMessage
};
To watch how the tasks being executed in realtime, you can activate the debug logging via the debug option.
flowa.run(context, {debug: true});
To create Flowa objects
FlowaA factory method to create Flowa objects
PromiseCreate a flow and execute it
PromiseExecute the flow
To create Flowa objects.
| Param | Type | Description |
|---|---|---|
| flow | Object | A compound task |
| name | String | A name for the flow (Optional) |
FlowaA 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) |
PromiseCreate 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) |
PromiseExecute 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) |
ETIMEDOUT) if the timeout is exeeded (type: Number).ETIMEDOUT) if the timeout is exeeded (type: Number).Boolean).Boolean) (default: console.log).This project is under the MIT license.
FAQs
Service level control flow for Node.js
The npm package flowa receives a total of 51 weekly downloads. As such, flowa popularity was classified as not popular.
We found that flowa demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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