I love mike bostock's stuff, but his code often makes me feel sorry for whoever has to deal with his code after him

   // Pick a location that’s not yet in the maze (if any).
    do if ((index0 = remaining.pop()) == null) return true;
    while (cells[index0] >= 0);

    // Perform a random walk starting at this location,
    previous[index0] = index0;
    walk: while (true) {
      i = index0 % width;
      j = index0 / width | 0;

      // picking a legal random direction at each step.
      direction = Math.random() * 4 | 0;
      if (direction === 0) { if (j <= 0) continue walk; --j; }
      else if (direction === 1) { if (j >= height - 1) continue walk; ++j; }
      else if (direction === 2) { if (i <= 0) continue walk; --i; }
      else { if (i >= width - 1) continue walk; ++i; }

note the braceless do while and the labeled jump statements