Проверка массива на число

const a = [ 
  [1,2,3], 
  ['a','b','c'], 
  [ 4,5,6], 
  ['d','e','f'], 
  [ 7,8,9], 
]; 
for (var i = 0; i < a.length; i++) { 
  for (var j = 0; j < a[i].length; j++) { 
    if (a[i][j] === +a[i][j]) 
      console.log(a[i][j], "- number"); 
    else if (typeof a[i][j] == "string") 
      console.log(a[i][j], "- string"); 
  } 
}