Changing React State Array at Specific Index

As the title suggests, I'm attempting to target an array inside of my state object but as you would guess if you ever tried. This isn't as straightforward as it sounds. I've looked through a couple of questions here (React: How do I update state.item[1] on setState? (with JSFiddle) and ReactJS - setState of Object key in Array) but neither are solving my problem.

What I need is to target a specific index inside of the noteData array, and update it according to whatever a user types into the <TextArea /> component. Not exactly sure why but my noteData array just read as an array with an empty string noteData = [''].

If you need a more in-depth look, you can go to https://stackblitz.com/edit/note-taking and fork the page and edit it yourself. The file structure is goofy to the say the least. I started using redux and decided against it halfway through.

state and functions TextArea

class NoteList extends Component {
  constructor(props) {
    super(props);
    this.state = {
      inputValue: '',
      noteName: [],
      noteData: [],
      selectedNote: []
    }
}

  handleInputValue(e) {
    this.setState({
      inputValue: e.target.value
    });
  }

  addNoteFunc(e) {
    this.setState({
      noteName: [ ...this.state.noteName, e.target.value ],
      noteData: [ ...this.state.noteData, '' ]
    });
  }

 // everytime the user types, change the value of noteData
  handleNoteData(e, index = this.state.selectedNote[0]) {
    const copyNoteData = Object.assign({}, this.state);
    copyNoteData.noteData[index] = e.target.value;

    this.setState(copyNoteData);
  }

  handleSelectedNote(index) {
    this.setState({
      selectedNote: [ index ]
    });
  }

<textarea 
  value={this.state.noteData[this.state.selectedNote[0]]}
  handleNoteData={(e, index) => this.handleNoteData(e, index)}
/>

The actual TextArea component

import React from 'react';

const TextArea = props => {
  return (
    <div className='textarea'>
      <textarea 
        value={props.value}
        onKeyDown={props.handleNoteData}
      />
    </div>
  );
}

export default TextArea;