Practical Introduction To Finite State Machines

A Practical Introduction to Finite State Machines

In this post, we will give you information about A Practical Introduction to Finite State Machines. Here we will give you detail about A Practical Introduction to Finite State Machines And how to use it also give you a demo for it if it is necessary.

A finite state machine is a fancy way to describe a very simple design pattern: there is a list of valid states, and a list of allowed transitions between states.

For example, JavaScript promises are state machines. A promise can be in one of 3 states:

Pending
Fulfilled
Rejected

There are only two allowed state transitions: pending to fulfilled, and
pending to rejected. Once a promise is fulfilled, it stays fulfilled forever.
You can represent this state machine using the below state machine diagram.

A state machine diagram usually represents states using circles or squares,
and transitions using lines or arrows.

A Basic Use Case With Mongoose

Suppose you’re building an app for moderating blog post comments.
Moderating comments can be represented by a state machine similar
to the one for promises. A comment can be in one of 3 states:

Pending
Approved
Rejected

You only want to display approved comments on your blog. But an admin
should have an easy way to load all pending comments. Here’s how
you might represent this using a Mongoose schema:

const schema = mongoose.Schema({
  state: {
    type: String,
    enum: ['Pending', 'Approved', 'Rejected'],
    required: true,
    default: 'Pending'
  },
  authorId: mongoose.ObjectId,
  comment: String
});

const Comment = mongoose.model('Comment', schema);

Loading all pending or all approved comments is easy using Mongoose’s find() function:

const pending = await Comment.find({ state: 'Pending' });

Here’s how the state machine diagram looks:

As the developer, you’re responsible for ensuring these state transitions
are respected. For example, you could expose 2 Express endpoints: one for
approving a comment, and one for rejecting a comment.

app.put('/comment/:id/approve', async function(req, res) {
  const comment = await Comment.findById(req.params.id);
  if (comment.state !== 'Pending') {
    return res.send(400).json({ message: 'Comment is not pending' });
  }
  comment.state = 'Approved';
  await comment.save();
  res.json({ ok: 1 });
});

app.put('/comment/:id/reject', async function(req, res) {
  const comment = await Comment.findById(req.params.id);
  if (comment.state !== 'Pending') {
    return res.send(400).json({ message: 'Comment is not pending' });
  }
  comment.state = 'Rejected';
  await comment.save();
  res.json({ ok: 1 });
});

JavaScript Fundamentals for Practical Introduction to Finite State Machines

JavaScript is a programming language that is used to create interactive web pages. It is a client-side scripting language, which means that it runs on the user’s browser. JavaScript can be used to add animation, interactivity, and functionality to web pages.

Here are some of the fundamentals of JavaScript:

Variables: Variables are used to store data. They are declared using the var keyword.
Data types: JavaScript has a variety of data types, including strings, numbers, booleans, objects, and arrays.
Operators: Operators are used to perform operations on data.
Control flow statements: Control flow statements allow you to control the order in which your code is executed.
Functions: Functions are blocks of code that can be reused.
Objects: Objects are used to store data in key-value pairs.
Arrays: Arrays are used to store data in a sequential order.
Events and event handlers: Events are notifications that are sent by the browser when something happens, such as when the user clicks on an element or moves the mouse over an element. Event handlers are functions that are called in response to an event.
DOM manipulation: The Document Object Model (DOM) is a tree-like structure that represents the elements of a web page. JavaScript can be used to manipulate the DOM to change the appearance or behavior of a web page.

These are just some of the fundamentals of JavaScript. There are many other concepts that you can learn as you continue to develop your skills.

Here are some resources that you can use to learn more about JavaScript:

Mozilla Developer Network (MDN): The MDN is a great resource for learning about JavaScript. It has a comprehensive reference guide, tutorials, and articles on a wide range of topics.
W3Schools: W3Schools is another great resource for learning about JavaScript. It has interactive tutorials and quizzes that can help you learn the basics of the language.
JavaScript.info: JavaScript.info is a website that provides in-depth tutorials on JavaScript. It also has a forum where you can ask questions and get help from other JavaScript developers.

I hope this helps!

Here are some additional tips for learning JavaScript:

Start with the basics: Before you start trying to build complex applications, it’s important to learn the basics of JavaScript. This includes things like variables, data types, operators, and control flow statements.
Practice regularly: The best way to learn JavaScript is to practice regularly. Try to find some time each day to work on JavaScript projects.
Get help from others: If you get stuck, don’t be afraid to ask for help from others. There are many online forums and communities where you can get help from other JavaScript developers.

With a little practice, you’ll be able to learn JavaScript and start building amazing web applications.

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