var unicodeString = "가나다라마바사아자차카타파하";

var unicodeString_large = "".padStart(30000, unicodeString);

var textEncoder = new TextEncoder();

​

const PREFIX_STR = "data:text/plain;base64,";

​

function toBase64FileReader( text ) {

  return new Promise( (resolve, reject) => {

    const reader = new FileReader();

    // data:text/plain;base64,...

    reader.onload = () => resolve(reader.result.substr(PREFIX_STR.length));

    reader.onerror = (err) => reject(err);

    reader.readAsDataURL(

      new Blob([ new TextEncoder().encode( text ) ], { type: "text/plain" })

    );

  });

}

​

function toBase64TextEcnder( text ) {

  return btoa( String.fromCharCode(...textEncoder.encode(text)));

}

​

function toBase64Unscape( text ) {

  return btoa(unescape(encodeURIComponent(text)));

}