TheAlgorithms/JavaScript · error · TypeError

Grid must be a non-empty array

Error message

Grid must be a non-empty array

What it means

Thrown by validateGrid() in the Rat-in-a-Maze solver before any backtracking begins. The solver indexes grid[y][x], so it requires an actual Array with at least one row; null, undefined, objects, primitives, or an empty array are all rejected up front.

Source

Thrown at Backtracking/RatInAMaze.js:26

 * Reference for this problem: https://www.geeksforgeeks.org/rat-in-a-maze-backtracking-2/
 *
 * Based on the original implementation contributed by Chiranjeev Thapliyal (https://github.com/chiranjeev-thapliyal).
 */

/**
 * Checks if the given grid is valid.
 *
 * A grid needs to satisfy these conditions:
 * - must not be empty
 * - must be a square
 * - must not contain values other than {@code 0} and {@code 1}
 *
 * @param grid The grid to check.
 * @throws TypeError When the given grid is invalid.
 */
function validateGrid(grid) {
  if (!Array.isArray(grid) || grid.length === 0)
    throw new TypeError('Grid must be a non-empty array')

  const allRowsHaveCorrectLength = grid.every(
    (row) => row.length === grid.length
  )
  if (!allRowsHaveCorrectLength) throw new TypeError('Grid must be a square')

  const allCellsHaveValidValues = grid.every((row) => {
    return row.every((cell) => cell === 0 || cell === 1)
  })
  if (!allCellsHaveValidValues)
    throw new TypeError('Grid must only contain 0s and 1s')
}

function isSafe(grid, x, y) {
  const n = grid.length
  return x >= 0 && x < n && y >= 0 && y < n && grid[y][x] === 1
}

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Pass a non-empty square 2D array of 0/1 values, e.g. [[1,0,1],[0,1,0],[0,0,1]].
2. If the grid comes from JSON or a fetch, verify Array.isArray(grid) && grid.length>0 before calling the solver.
3. Ensure the variable is not shadowed or accidentally set to undefined by a failed map/assignment.

Example fix

// before
const path = solveRatInAMaze(parsed ?? [])
// after
const path = Array.isArray(parsed) && parsed.length
  ? solveRatInAMaze(parsed)
  : null

function isValidMazeGrid(g) {
  if (!Array.isArray(g) || g.length === 0) return false;
  const n = g.length;
  return g.every(r => Array.isArray(r) && r.length === n && r.every(c => c === 0 || c === 1));
}
// if (isValidMazeGrid(grid)) solve(grid);

/** @param {unknown} g @returns {g is number[][]} */
function isSquareBinaryGrid(g) {
  if (!Array.isArray(g) || g.length === 0) return false;
  const n = g.length;
  return g.every(r => Array.isArray(r) && r.length === n &&
    r.every(c => c === 0 || c === 1));
}

try { solve(grid); }
catch (e) {
  if (e instanceof TypeError && /non-empty array/.test(e.message)) {
    // handle bad/missing grid
  } else throw e;
}

When it happens

Trigger: Calling solve()/validateGrid with null, undefined, [], {}, a number, a string, a Set, or any non-Array value. Also triggered when a JSON parse returns null/empty and that result is passed straight through.

Common situations: Loading the maze from a JSON config that failed to parse, defaulting an unset option to [] (empty), or passing a matrix-library wrapper / typed array instead of a plain Array of Arrays.

Related errors

• Grid must be a square
• Grid must only contain 0s and 1s
• LFUCache ERROR: The Capacity is 0
• Both keyword and message must be specified
• Invalid keyword!

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/42f2fb32e41f2365. Report an issue: GitHub.