[Javascript] Turing Machine

tm.js

function tm(tape, transform, startState, endStates, i){
  currState = startState; 
  while(currState is not in endStates){
    sym = (tape[i])? tape[i]: 'Blank';
    state = transform[currState][sym];
    if(!state) return 'Not Halting';
    tape[i] = state.w;   // write sym
    i += state.m;        // move tape
    currState = state.n; // move to next state
  }
  return tape;
}