fhex | A Full-Featured HexEditor compatible with Linux/Windows/MacOS | Editor library

The reason you get both numbers twice in the output is because you passed fhex into replace, where it expected a string, so it converted [90, 131] into "90,131". Instead, you want to pass the converted number in, which then gets converted to the string you actually want.

An additional problem is that if you pass the hexadecimal regex in as the first parameter to replace, then it will match all the hexadecimal numbers, so you want to pass something that only matches the string you want to replace with the number you currently have. Luckily, the string itself does that! So instead of replacing each fhex[i] value with a number, if you keep the string around, and put the number in a separate variable, you can pass the original string and the new number value into replace like so: