extractText method
Extract text from a given cfi range,
Implementation
Future<EpubTextExtractRes> extractText({
///start cfi
required startCfi,
///end cfi
required endCfi,
}) async {
checkEpubLoaded();
pageTextCompleter = Completer<EpubTextExtractRes>();
await webViewController?.evaluateJavascript(
source: 'getTextFromCfi("$startCfi","$endCfi")');
return pageTextCompleter.future;
}