Sample code for implementing finite state machine in JavaScript

Finite State Machine (FSM) is a mathematical model used to describe the behavior of a system in different states. In front-end development, finite state machines can be used to manage complex UI interaction logic, such as games, form verification and other scenarios.

Here is an example of a simple JavaScript implementation of a finite state machine:

class FiniteStateMachine {
  constructor() {
     = {};
     = null;
     = [];
     = null;
  }
  // Set initial state  setStartState(name) {
     = name;
     = name;
  }
  // Add a state transition processor  addHandler(state, event, newState, action) {
    if (![state]) {
      [state] = {};
    }
    [state][event] = { newState, action };
  }
  // Set the end state  addEndState(state) {
    (state);
  }
  // Process events and perform state transitions  handleEvent(event) {
    if ( === null) {
      throw new Error('FiniteStateMachine has no start state.');
    }
    const handler = [][event];
    if (!handler) {
      throw new Error(`Cannot handle event ${event} in state ${}.`);
    }
    // Execute the action before state transition    if () {
      ();
    }
    // Perform state transitions     = ;
    // Check whether the end state is reached    if (()) {
      ('Reached an end state:', );
    }
  }
}

Example of usage:

// Create a finite state machine instanceconst fsm = new FiniteStateMachine();
// Set the initial state to 'state1'('state1');
// Add state transition processor and action('state1', 'event1', 'state2', () =&gt; ('Moving from state1 to state2'));
('state2', 'event2', 'state3', () =&gt; ('Moving from state2 to state3'));
('state3', 'event3', 'state1', () =&gt; ('Moving from state3 to state1'));
// Set the end state (optional)('state3');
// Process events and perform state transitions('event1'); // Output: Moving from state1 to state2('event2'); // Output: Moving from state2 to state3('event3'); // Output: Moving from state3 to state1 and Reached an end state: state1

This simple finite state machine implementation can be expanded and optimized according to your specific needs. For example, you can add more states, events, and actions, or use more complex data structures to store state transition rules.

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