In case you meant const a = 1,25; instead of const a = 1.25; , you are probably out of luck (Babel plugin at best).
If you meant const a = parseFloat('1,25'); instead of const a = parseFloat('1.25') , you can get there using string.replace or a regex (depending on your circumstances): const a = parseFloat('1,25'.replace(',', '.')); (which might not be the sanest solution available :D)