See: https://cses.fi/problemset/task/1071

number-spiral.js

function layer(N) {
  return Math.ceil(Math.sqrt(N));
}

function layerRange(L) {
  const start = Math.pow(L - 1, 2) + 1;
  const end = Math.pow(L, 2);

  return [start, end];
}

function direction(L, axis) {
  switch (axis) {
    case "y": {
      return L % 2 === 0 ? 1 : -1;
    }
    case "x": {
      return L % 2 === 0 ? -1 : 1;
    }
    default: {
      throw new Error(`Invalid axis argument supplied: ${axis}`);
    }
  }
}

function coord(N, axis) {
  const L = layer(N);

  const [start, end] = layerRange(L);
  const sequenceIndex = N - start;
  const midIndex = (end - start) / 2;

  const D = direction(L, axis);
  switch (D) {
    case 1: {
      if (sequenceIndex <= midIndex) {
        return sequenceIndex + 1;
      }
      return L;
    }
    case -1: {
      if (sequenceIndex > midIndex) {
        return L + D * (sequenceIndex - midIndex);
      }
      return L;
    }
    default: {
      throw new Error(`Invalid direction generated: ${direction}`);
    }
  }
}

function y(N) {
  return coord(N, "y");
}

function x(N) {
  return coord(N, "x");
}

function f(N) {
  return [y(N), x(N)];
}

// --------------------

function* range(start, end) {
  for (let i = start; i <= end; i++) {
    yield i;
  }
}

function printGrid(grid) {
  console.table(grid);
}

// --------------------

console.log("==================");

const grid = [];
for (let N of range(1, 25)) {
  console.debug(`${N} = ${f(N)}`);

  const [y, x] = f(N);
  if (!grid[y - 1]) {
    grid[y - 1] = [];
  }
  grid[y - 1][x - 1] = N;
}

printGrid(grid);

This is actually a solution to a different problem than the one posed. In the problem posed on cses.fi you are passed (y, x) and must produce n -- while above we've passed n to work out (y, x).