Get/set file encoding with javascript's FileReader
If your HTML page is in UTF-8 and your file is in ISO-8859-1.
This is working:
reader.readAsText(file, 'ISO-8859-1');I don't have any Windows-1251 file so I was not able to test it but it looks like that the 'CP1251' is supported (by Google Chrome at least), so:
reader.readAsText(file, 'CP1251');If none of this is working. Then you should change the formatting manually. Unfortunately, I am not aware of any JavaScript library that does the trick.
From the unicode mapping here and from Delan Azabani answer, you should manage to build a function that convert char by char your string in CP1251 to UTF-8.