Preheat oven to 350°F. Grease a 9 x 5-inch loaf pan.
Sift or whisk flour, cocoa, baking soda, baking powder and salt in a large bowl. Add brown sugar and sugar; stir to combine. Beat bananas, butter, corn syrup, eggs and vanilla in a separate bowl. Add banana mixture and chocolate chips to dry ingredients; fold gently until just combined.
Bake 50 to 55 minutes, or until toothpick inserted in center comes out clean (unless you hit a chocolate chip). Cool 10 minutes; remove from pan and finish cooling on wire rack.