FileReader .result is undefined

`FileReader.result` is undefined until the `load` event fires on the `FileReader` object. This is because the `FileReader` API reads files asynchronously and the `load` event is fired only after the file has been completely read.

Here's an example of how to use `FileReader` to read a file and display its contents:

const fileInput = document.querySelector('input[type="file"]');
fileInput.addEventListener('change', (event) => {
  const file = event.target.files[0];
  const reader = new FileReader();
  reader.addEventListener('load', (event) => {
    const fileContent = event.target.result;
    console.log(fileContent);
    // Do something with the file content
  });
  reader.readAsText(file);
});

In this example, we're listening for the `change` event on a file input element, creating a new `FileReader` object, and using the `readAsText` method to read the contents of the selected file. Once the file has been read, the `load` event is fired and we can access the file content using the `result` property on the `FileReader` object.