===== ISTEM =====
Solve the following programming task.

TASK: TIK Register Machine

Write a function 'runTik(program)' that runs a program written in TIK, a small made-up language, and returns an array of the numbers it outputs.

Program text:
- Instructions are separated by newlines. Leading and trailing spaces on a line are ignored.
- Lines that are empty (or only spaces) and lines whose first non-space character is '#' are ignored and are not instructions.
- Within an instruction, tokens are separated by one or more spaces.

Machine:
- There are four registers named a, b, c and d. All start at 0.
- Every value stored in a register is reduced to the range 0..999 by taking it modulo 1000, always giving a non-negative result (for example -1 becomes 999 and 1003 becomes 3).
- An integer literal is an optional '-' followed by one or more digits ('+5' and '5.0' are not valid).
- An operand written as X below is either a register name or an integer literal. Its value is the register's value, or the literal reduced to 0..999 in the same way.

Instructions (R must be a register name, N must be an integer literal):
- set R X: R becomes the value of X.
- add R X: R becomes R plus the value of X.
- mul R X: R becomes R times the value of X.
- out X: appends the value of X to the output.
- jmp X N: if the value of X is not 0, the next instruction is the one N instructions away from this one (N may be negative; ignored lines are not counted). Otherwise execution continues with the next instruction.
Instruction names and register names are lowercase; anything else is invalid.

Running:
- Before running anything, check the whole program. If any line that is not ignored is not a valid instruction (unknown name, wrong number of operands, or an invalid register, literal or operand), throw an Error whose message is 'bad instruction at line K', where K is the 1-based line number of the first such line in the original text, counting ignored lines too. In that case nothing is run.
- Execution starts at the first instruction and stops normally when the next instruction position is before the first instruction or after the last one.
- A program may execute at most 10,000 instructions. If it has not stopped after executing 10,000 instructions, throw an Error with the message 'step limit'.

STARTER CODE (javascript):
function runTik(program) {
  // Write your code here
}

module.exports = { runTik };


RULES:
- Keep the function name and signature EXACTLY as given.
- Return working code only. No explanations.
- Put the code in a single ``` block.
- Try to solve it first. If you genuinely cannot, write only this single
  line instead of producing faulty code: CANNOT_SOLVE

===== HAM YANIT =====
```javascript
function runTik(program) {
  const isReg = (tok) => tok === 'a' || tok === 'b' || tok === 'c' || tok === 'd';
  const isIntLiteral = (tok) => /^-?\d+$/.test(tok);
  const isOperand = (tok) => isReg(tok) || isIntLiteral(tok);

  const lines = program.split(/\r?\n/);
  const instructions = [];

  for (let i = 0; i < lines.length; i++) {
    const trimmed = lines[i].trim();
    if (trimmed === '' || trimmed.startsWith('#')) {
      continue;
    }

    const tokens = trimmed.split(/\s+/);
    const op = tokens[0];
    let valid = false;

    if (op === 'set' || op === 'add' || op === 'mul') {
      if (tokens.length === 3 && isReg(tokens[1]) && isOperand(tokens[2])) {
        valid = true;
      }
    } else if (op === 'out') {
      if (tokens.length === 2 && isOperand(tokens[1])) {
        valid = true;
      }
    } else if (op === 'jmp') {
      if (tokens.length === 3 && isOperand(tokens[1]) && isIntLiteral(tokens[2])) {
        valid = true;
      }
    }

    if (!valid) {
      throw new Error(`bad instruction at line ${i + 1}`);
    }

    instructions.push({
      op,
      tokens: tokens.slice(1)
    });
  }

  const mod1000 = (n) => ((n % 1000) + 1000) % 1000;

  const registers = { a: 0, b: 0, c: 0, d: 0 };
  const getVal = (x) => {
    if (isReg(x)) {
      return registers[x];
    }
    return mod1000(parseInt(x, 10));
  };

  const output = [];
  let pc = 0;
  let steps = 0;

  while (pc >= 0 && pc < instructions.length) {
    if (steps === 10000) {
      throw new Error('step limit');
    }

    const { op, tokens } = instructions[pc];
    steps++;

    if (op === 'set') {
      registers[tokens[0]] = getVal(tokens[1]);
      pc++;
    } else if (op === 'add') {
      registers[tokens[0]] = mod1000(registers[tokens[0]] + getVal(tokens[1]));
      pc++;
    } else if (op === 'mul') {
      registers[tokens[0]] = mod1000(registers[tokens[0]] * getVal(tokens[1]));
      pc++;
    } else if (op === 'out') {
      output.push(getVal(tokens[0]));
      pc++;
    } else if (op === 'jmp') {
      const cond = getVal(tokens[0]);
      if (cond !== 0) {
        pc += parseInt(tokens[1], 10);
      } else {
        pc++;
      }
    }
  }

  return output;
}

module.exports = { runTik };
```