AI solution for JavaScript Coding Question on BFE.dev
9. decode message

Here's one possible solution in JavaScript:

function decodeMessage(arr) {
  const numRows = arr.length;
  const numCols = arr[0].length;
  let result = "";

  let row = 0;
  let col = 0;
  let goingDown = true;

  while (result.length < numRows * numCols) {
    result += arr[row][col];

    if (goingDown) {
      if (row === numRows - 1) {
        goingDown = false;
        col++;
      } else if (col == 0) {
        goingDown = false;
        row++;
      } else {
        row++;
        col--;
      }
    } else {
      if (col === numCols - 1) {
        goingDown = true;
        row++;
      } else if (row === 0) {
        goingDown = true;
        col++;
      } else {
        row--;
        col++;
      }
    }
  }

  return result;
}

We first get the number of rows and columns from the input array. We then initialize a few variables: result to store the decoded message, row and col to keep track of our current position, and goingDown to determine whether we're currently moving down-right or up-right.

We then enter a loop that will continue until we've processed all characters in the input array. At each step, we append the current character to the result.

If we're moving down-right, we check if we're at the bottom row or leftmost column. If so, we switch to moving up-right by incrementing the column or row respectively. Otherwise, we continue moving down-right by incrementing the row and decrementing the column.

If we're moving up-right, we check if we're at the rightmost column or top row. If so, we switch to moving down-right by incrementing the row or column respectively. Otherwise, we continue moving up-right by decrementing the row and incrementing the column.

Finally, we return the resulting message. Note that if the input array is empty or has no characters, the function will return an empty string.