JavaScript: CSV Get Headers from input stream using ArrayBuffer

gistfile1.js

function CSVImportGetHeaders()
{
    // Get our CSV file from upload
    var file = document.getElementById('CSVUpload').files[0]

    // Instantiate a new FileReader
    var reader = new FileReader();

    // Read our file to an ArrayBuffer
    reader.readAsArrayBuffer(file);

    // Handler for onloadend event.  Triggered each time the reading operation is completed (success or failure) 
    reader.onloadend = function (evt) {
        // Get the Array Buffer
        var data = evt.target.result;

        // Grab our byte length
        var byteLength = data.byteLength;

        // Convert to conventional array, so we can iterate though it
        var ui8a = new Uint8Array(data, 0);

        // Used to store each character that makes up CSV header
        var headerString = '';

        // Iterate through each character in our Array
        for (var i = 0; i < byteLength; i++) {
            // Get the character for the current iteration
            var char = String.fromCharCode(ui8a[i]);

            // Check if the char is a new line
            if (char.match(/[^\r\n]+/g) !== null) {
                
                // Not a new line so lets append it to our header string and keep processing
                headerString += char;
            } else {
                // We found a new line character, stop processing
                break;
            }
        }
        
        // Split our header string into an array
        window.headers = headerString.split(',');
        debugger;

        // Convert entire ArrayBuffer to string --avoided so not all of ArrayBuffer would have to come into memory
        //var arrayToStream = String.fromCharCode.apply(null, new Uint8Array(data));
        // Splits on any new line characters and grabs first row, assuming it is headers
        //var firstLine = arrayToStream.match(/[^\r\n]+/g)[0];
        // Splits on a delimiter
        //var delimiterSplit = firstLine.split(',');
    };

    
}

nice job
how can i get second line like headerString ?