FileReader - which encodings are supported?

Question

Want to simlpy read user-input files as text.

Can rely on modern browser usage, so I use FileReader for that (which works like a charm).

reader.readAsText(myfile, encoding);

I know that encoding defaults to UTF-8.

But as my users will upload files from various sources (Windows, Mac, Linux) and various browsers I ask the user to provide the encoding via a select box.

So e.g. for a western european windows text file I expect the user to choose e.g. windows-1252.

I was not able to find a list of supported encodings for FileReader (assuming this is at least depending on the browser).

I am not asking to auto-determine the encoding, I just want to fill my select box in a way like:

<select id="encoding">
   <option value="windows-1252">Windows (Western Latin)</option>
   <option value="utf-8">UTF-8</option>
   <option value="...">...</option>
</select>

So my questions are:

1. Where do I get a list of supported encodings to fill the option values?
2. How to determine the exact writing of those values (is it 'utf8' or 'UTF-8' or...) and are those depending on the OS / browser?
3. Does readAsText(myfile, unsupportedEncoding) throw any error which I can catch if encoding is not supported?

I'd prefer not to use any major 3rd party libraries for that.

Bonus Question:

Is there a simple way to get meaningful translations of the values, e.g. cp10029 means Mac (Central European)?

Answer 1

1. Encoding standarts - https://github.com/whatwg/encoding/ (in JSON format - https://github.com/whatwg/encoding/blob/master/encodings.json. Use values from fields "labels")

2. Encoding parameter is not case sensitive.

3. NO, readAsText(myfile, unsupportedEncoding) not throw any error. The function simply uses the default encoding("utf8").

   window.onload = function() {
   
       //Check File API support
       if (window.File && window.FileList && window.FileReader) {
           var filesInput = document.getElementById("files");
   
           filesInput.addEventListener("change", function(event) {
   
               var files = event.target.files; //FileList object
               var output = document.getElementById("result");
   
               for (var i = 0; i < files.length; i++) {
                   var file = files[i];
   
                   //Only plain text
                   if (!file.type.match('plain')) continue;
   
                   var picReader = new FileReader();
   
                   picReader.addEventListener("load", function(event) {
   
                       var textFile = event.target;
   
                       var div = document.createElement("div");
   
                       div.innerText = textFile.result;
   
                       output.insertBefore(div, null);
   
                   });
                   //Read the text file
                   picReader.readAsText(file, "cP1251");
               }
   
           });
       }
       else {
           console.log("Your browser does not support File API");
       }
   }
   

Demo

To get translations of the values you can use JSON file (https://github.com/whatwg/encoding/blob/master/encodings.json), parameter "heading" and "name".