Preheat the oven to 375 degrees F (190 degrees C). Sift together the flour, baking powder, baking soda and salt, set aside.
In a large bowl, cream together the butter, sugar and brown sugar. Beat in the eggs, one at a time, then stir in the vanilla and mashed banana. Mix in the dry ingredients until just blended, then fold in chocolate chips. Drop by rounded spoonfuls onto prepared cookie sheets.
Bake for 11 to 13 minutes in the preheated oven. Allow cookies to cool on baking sheet for 5 minutes before removing to a wire rack to cool completely.