Javascript one-liner to calculate total minesweeper neighbours

mines.js

var m = [
  [' ',' ',' ',' ',' '],
  [' ',' ',' ',' ',' '],
  ['X',' ',' ',' ',' '],
  [' ','X',' ',' ',' '],
  [' ',' ','X',' ',' '],
]

var m = [
  [' ',' ','X'],
  [' ',' ','X'],
  [' ','X',' '],
  ['X',' ',' '],
]

// Polyfill for ECMA 2019
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat
if (!Array.prototype.flat) {
  Array.prototype.flat = function () {
    return this.reduce((acc, val) => acc.concat(val), []);
  }
}

s = m.map(
  (r,i) => r.map(
    (c,j) => c=='X' ? c :
      [,...m].splice(i,3).map(r=>[,...r].splice(j,3)).flat().filter(v=>v=='X').length
  )
)

s.forEach(r => console.log('| ' + r.join(' | ') + ' |'))

out.txt

| 0 | 2 | X |
| 1 | 3 | X |
| 2 | X | 2 |
| X | 2 | 1 |