How to Implement State Machines in Your Code

If you're anything like me, you've occasionally found yourself drowning in a sea of spaghetti code. You know what I mean - those deeply nested if/else statements, those methods that stretch off into infinity, those functions whose output seems to depend on the fickle whims of chance.

It's not a fun place to be. If you've ever spent hours scrolling through your own code, trying to figure out why that one edge case isn't working, you know what I'm talking about.

The good news is that there's a better way. It's called a state machine, and it's a powerful tool for gaining control over your code. In this article, we'll go over what state machines are, how they work, and how you can implement them in your own code.

What is a State Machine?

At its core, a state machine is a system that can exist in a finite number of states, and can transition between those states based on some set of rules.

Think of a vending machine. When you approach it, it's in a "waiting" state, waiting for you to insert some money. Once you insert money, it transitions to a "selecting" state, where you can use the buttons to select which item you want. Finally, when you hit the "dispense" button, it transitions to a "dispensing" state, where it dispenses your chosen item and returns to the "waiting" state.

At each step of the way, the vending machine has a set of rules that determine which state it should transition to next. For example, if you insert insufficient money, it might transition back to the "waiting" state and display an error message.

It's similar to how traffic lights work. A traffic light is a state machine with three states - "red," "yellow," and "green." It transitions between those states based on a set of rules - for example, when the light is green, it will transition to yellow after a fixed period of time, and from yellow to red after another fixed period.

So how can we use this concept in our own code?

Why Use State Machines?

The benefits of using state machines in your code are many. For one thing, they can greatly simplify your logic. If you're dealing with a set of complex rules that determine which action to take next, state machines can help you break those rules down into discrete states and transitions.

Additionally, state machines can make your code more robust and easier to test. Because each state is its own discrete entity with its own set of rules, you can test each state independently to make sure it's working correctly. This can make debugging much easier and less time-consuming.

Finally, state machines can make your code more scalable. As your codebase grows and becomes more complex, state machines can help you keep your code organized and maintainable. They provide a clear, structured way to handle complex logic and state transitions.

How State Machines Work

At a basic level, state machines consist of two main components - states and transitions.

A state is a particular condition or situation that your program can be in. For example, a state might represent the moment when a user is logged in, or when an application is in "error" mode.

Transitions are the ways in which your program can move between those states. For example, a program might transition from "logged in" to "logged out" when a user clicks the "log out" button.

The key with state machines is that you define the rules for how those transitions happen. For example, maybe the "logged in" state can only transition to "logged out" if the user explicitly clicks the "log out" button. You might also define conditions that must be satisfied for a transition to take place - maybe the user can only log out if they haven't made any in-app purchases in the last 24 hours.

Implementing State Machines in Your Code

So how can you start implementing state machines in your own code? Here are the steps you'll need to follow:

Step 1: Identify the States

The first step is to identify the states that your program can be in. This will depend on your specific use case, but some common states might include:

Step 2: Define the Transitions

Once you've identified your states, it's time to define the transitions between them. This will involve determining under what conditions your program should move from one state to another.

For example, maybe your program transitions from "loading" to "displaying data" when it receives a successful API response from a server. Or maybe it transitions from "processing user input" to "saving data" when the user clicks the "submit" button on a form.

Step 3: Implement the State Machine

With your states and transitions defined, it's time to implement the state machine itself. There are many different ways to do this, but one common approach is to use a switch statement.

Here's an example:

let currentState = 'loading';

function transition(state, data) {
  switch (state) {
    case 'loading':
      return data ? 'displaying data' : 'error';
    case 'displaying data':
      return 'waiting for user input';
    case 'error':
      return 'loading';
    case 'waiting for user input':
      return 'processing user input';
    case 'processing user input':
      return 'saving data';
    case 'saving data':
      return 'displaying data';
      throw new Error(`Invalid state: ${state}`);

currentState = transition(currentState, {});


In this example, we've defined six states and the rules for transitioning between them. We've also defined a transition function that takes a current state and some data, and returns the next state based on the rules we've defined.

When we run this code, we can see that it starts in the "loading" state, then transitions to the "error" state (because we haven't provided any data), and then back to the "loading" state.

Of course, this is a very simple example. In real-world scenarios, your state machine will likely be much more complex, with many more states and transitions.

Step 4: Incorporate the State Machine into Your Code

Once you've implemented your state machine, it's time to incorporate it into your code. This will depend on your specific use case, but some common approaches might include:


State machines are a powerful tool for gaining control over complex logic and transitions in your code. By breaking down your code into discrete states and transitions, you can simplify your logic, make your code more robust and testable, and ensure that it remains scalable as your codebase grows.

So if you've been struggling with spaghetti code and complex logic, give state machines a try. You might just find that they're the answer you've been looking for.

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Written by AI researcher, Haskell Ruska, PhD ( Scientific Journal of AI 2023, Peer Reviewed