Frontend problems really are something else. First, a number may include letters and does not correspond to real numbers. Second, JS thought it was a good idea

Frontend problems really are something else. First, a number may include letters and does not correspond to real numbers. Second, JS thought it was a good idea to not care about the datatypes. Then the worst. The mess created by decimals and commas having different meanings in different langs and cultures. A bug I see a couple of times per year and a freaking terrible one cause users enter decimal numbers that are 100 times smaller or bigger than intended.