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 !
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 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.
npm install --save flowa
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.
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.
function task1(context) {
// Do something !!
}
You can terminate the flow (skip executing the remaining tasks) by calling the done method.
function task1(context, callback) {
this.done();
callback();
}
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();
}
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();
}
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
*/
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
};
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
Skip the remaining tasks
Jump into another task under the same parent after executing the current task
A new instance from the class
Taskis created for each execution for each task.
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) (default: true).Boolean) (default: false).Boolean) (default: console.log).Skip the remaining tasks. Check Terminating The Flow.
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 |
This project is under the MIT license.
FAQs
Service level control flow for Node.js
The npm package flowa receives a total of 13 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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