Parser generator created in https://bravotic.com/dev/stdscr/index.php/2022/11/13/making-a-parser-generator-doesnt-have-to-be-hard/

parser.js

// The following is public domain, go wild.
// If you could however, please at least keep the blog URL in it if you use it verbaitum
// https://bravotic.com/dev/stdscr/index.php/2022/11/13/making-a-parser-generator-doesnt-have-to-be-hard/

// Step 1: Lets get a list of tokens
// Our list of tokens
var tokens = ["Hello", "Hi", "Goodbye", "Good", "World", "Wordlist"];

// Step 2: Create the trees
// We need to create a 'state' which holds the possible next letters, and a state for those as well
var initialState = {
        id: 0,
        next: []
};

// Keep track of how many states we have made for code generation later
var stateCounter = 0;

// Loop through our tokens
for(let i = 0; i < tokens.length; i++){
  
  // Our current token we are checking
  let currentToken = tokens[i];
  
  console.log("Current token: " + currentToken);
  
  // Reset to the initial state since we are on a new token
  let currentState = initialState;
  
  // Now loop through every letter in our token
  letterLoop: for(let j = 0; j < currentToken.length; j++){
    
    // Our current token letter
    let currentLetter = currentToken.at(j);
    
    // Go through every possible next letter
    for(let k = 0; k < currentState.next.length; k++){
      
      let possibleNextLetter = currentState.next[k];
      // If the possible next letter is our current letter, we follow it
      if(possibleNextLetter.letter == currentLetter){
        
        console.log("Found branch for: " + currentLetter);
        
        // Set the new current state to the branch we are following
        currentState = possibleNextLetter.state;
        
        // Go back to the letter loop
        continue letterLoop;
      }
    }
    
    console.log("Adding " + currentLetter);

    // If we get down here, its because we couldn't find a branch, so we need to add one
    currentState.next.push({
      letter: currentLetter,
      state: {
        id: ++stateCounter,
        next: []
      }
    });
    // Now set our state to the new state we made
    currentState = currentState.next.at(-1).state;
    console.log("ID: " + currentState.id);
  }
  
  console.log("Adding end of word marker");
  
  // Add our end of word marker, this contains the token number we return
  currentState.next.push({
    letter: 0,
    state: {
        id: ++stateCounter,
        next: []
    },
    token: i + 1
  });
}

// Step 3: Code generation
console.log("BELOW IS THE GENERATED PARSER CODE");

// Print the head to our function

// function parse(token){
//   let i = 0;
//   let state = 0;
//   switch(state){
console.log("function parse(token){");
console.log("\tlet i = 0;");
console.log("\tlet state = 0;");
console.log("\twhile(true){");
console.log("\t\tswitch(state){");

// Now go though each state and print out the imporant bits
// To do this I'll simply create a recursive function.

function printState(state){
 
  // Print our case
  console.log("\t\t\tcase " + state.id + ":");

  // Make our case for the next letter
  console.log("\t\t\t\tswitch(token.at(i)){");
  
  // And our conditions
  for(let i = 0; i < state.next.length; i++){

    let condition = state.next[i];

    // If our letter is 0, we are at the end of the string, in Javascript, the string.at should return undefined at the end, so we check for that
    if(condition.letter == 0){
     // If we are actually at the end of the string, return our token number
     console.log("\t\t\t\t\tcase undefined: return " + condition.token + ";");
    }
    else{
      // Otherwise make it so we go to the next state

      // case 'nextLetter':
      //   i++;
      //   state = nextStateId;
      //   break;
      console.log("\t\t\t\t\tcase '" + condition.letter + "':");
      console.log("\t\t\t\t\t\ti++;");
      console.log("\t\t\t\t\t\tstate = " + condition.state.id + ";");
      console.log("\t\t\t\t\t\tbreak;");
    }
  }
  // Make sure if we can't branch anymore, we return 0 so we don't hit an infinite loop
  
  // defualt: reutrn 0;
  console.log("\t\t\t\t\tdefault: return 0;");

  // And finally just close up the switch/case and this current case for the state machine.
  console.log("\t\t\t\t}");
  console.log("\t\t\tbreak;");
  
  // Now go through every next state and print it out again
  for(let i = 0; i < state.next.length; i++){
    // recursion is fun
    // recursion is fun
    // recursion is fun
    // recursion is fun
    printState(state.next[i].state);
  }
}

// Call the function on the initial state and it should go through everything 
printState(initialState);

// Now finish up the function
console.log("\t\t}");
console.log("\t}");
console.log("}");

// Now everything is done