NFA

nfa.js

// [ab]*a[ab][ab] 
f = {
  '0':{'a':[0,1], 'b':[0]},
  '1':{'a':[2], 'b':[2]},
  '2':{'a':[3], 'b':[3]},
}
// f[theta][sigma]

const final = new Set([3])
let state = 0;
let result = false;
const str = "baaba";

for (let j=0; j<str.length;j++){
  const it = str[j];
  
  for (let i=0; i<f[state][it].length;i++){
    if(final.has(f[state][it][i])) {
      result = true;
      break;
    }
    state = f[state][it][i]
  }
  if (result) {
    break;
  } 
}

console.log('result: ', result);