Question

I was wondering what the neatest way would be to convert (from Python) a list comprehension into Javascript. Is there anything which will make this readable and not a mess?

    non_zero_in_square = [ grid[row][col]
                           for row in range(start_row, start_row+3)
                           for col in range(start_col, start_col+3)
                           if grid[row][col] is not 0
                         ]

This is quite a good example of a list comprehension, as it has multiple fors and and an if.

I should add that the range bit is covered here (I can’t live without range).

Answer 1

Well it would be somewhat messy to do this with the .map() method, because the outer calls really need to return arrays. Thus you’re probably best with the pedestrian:

var nonZero = [];
for (var row = startRow; row < startRow + 3; ++row)
  for (var col = startCol; col < startCol + 3; ++col)
    if (grid[row][col] !== 0) nonZero.push(grid[row][col];