FileReaderSync is not defined

`FileReaderSync` is not available in web browsers anymore. It has been removed from the Web APIs standard due to its blocking nature, which may cause performance issues and freeze the browser UI.

Instead of using `FileReaderSync`, you can use the asynchronous `FileReader` API to read files in the browser. Here's an example:

const fileInput = document.getElementById('fileInput');

fileInput.addEventListener('change', (event) => {
  const file = event.target.files[0];

  const reader = new FileReader();
  
  reader.onload = () => {
    console.log(reader.result); // Process the file content here
  };

  reader.readAsText(file);
});

This code listens for a file selection event on a file input element with an id of `fileInput`. When a file is selected, it creates a `FileReader` instance, sets the `onload` callback to process the file content, and calls the `readAsText` method to read the file as text. Once the file is read, the `onload` callback will be called with the file content as a string.