JavaScript Error

// Copyright 2024 T&J Divisions, LLC	
// Designed and Developed by Tim Tolbert
// All Rights Reserved
namespace TestProgram
{
    public partial class Form1 : Form
    {
        int currentFile = 0;
        List<string> files = new List<string>();

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            // manually add the MouseWheel event to the PictureBox control
            pictureBox1.MouseWheel += new System.Windows.Forms.MouseEventHandler(PictureBox1_MouseWheel);

            // initialize open file dialog
            openFileDialog1.InitialDirectory = "c:\\temp\\";
            openFileDialog1.FileName = "";

            // set filter to image files only
            openFileDialog1.Filter = "Image Files(*.BMP;*.JPG;*.GIF;*.PNG)|*.BMP;*.JPG;*.GIF;*.PNG|" +
                                    "Bitmap (*.BMP)|*.BMP|" +
                                    "Jpeg (*.JPG)|*.JPG|" +
                                    "Animation (*.GIF)|*.GIF|" +
                                    "Portable Network Graphic (*.PNG)|*.PNG";
            
            // set default button states
            buttonPrevious.Enabled = false;
            buttonNext.Enabled = false;

            // clear feedback label
            feedbackLabel.Text = "";
        }

        private void buttonNext_Click(object sender, EventArgs e)
        {
            viewNextImage();
        }

        private void buttonOpen_Click(object sender, EventArgs e)
        {
            // prompt user to select an image file to open
            openFileDialog1.ShowDialog(this);
        }

        private void buttonPrevious_Click(object sender, EventArgs e)
        {
            viewPreviousImage();
        }

        private void openFileDialog1_FileOk(object sender, System.ComponentModel.CancelEventArgs e)
        {
            // display selected file path
            textBox1.Text = openFileDialog1.FileName;

            // get selected directory path
            string tempDir = Path.GetDirectoryName(openFileDialog1.FileName);
            if(tempDir.EndsWith("\\") == false)
            {
                tempDir += "\\";
            }

            // get current filter
            string[] currentFilters = openFileDialog1.Filter.Split("|")[((openFileDialog1.FilterIndex - 1) * 2) + 1].Split(";");

            // get all of the image file paths from this directory
            files.Clear();
            foreach (string filter in currentFilters)
            {
                // upper case
                files.AddRange(Directory.GetFiles(tempDir, filter.ToUpper(), SearchOption.TopDirectoryOnly).ToList());

                // lower case
                files.AddRange(Directory.GetFiles(tempDir, filter.ToLower(), SearchOption.TopDirectoryOnly).ToList());
            }

            // get index of the selected file path
            currentFile = files.IndexOf(openFileDialog1.FileName);

            // display this file in the picturebox
            try
            {
                pictureBox1.Load(openFileDialog1.FileName);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

            // check if should enable or disable the previous and next buttons
            if (files.Count > 1)
            {
                buttonPrevious.Enabled = true;
                buttonNext.Enabled = true;
            }
            else
            {
                buttonPrevious.Enabled = false;
                buttonNext.Enabled = false;
            }

            // display current file number
            feedbackLabel.Text = Convert.ToString(currentFile + 1) + " of " + files.Count.ToString();

        }

        private void PictureBox1_MouseWheel(object sender, MouseEventArgs e)
        {
            // precheck to ensure some image is loaded
            if (files.Count <= 1) { return; }

            // check if mouse wheel scrolled up or down
            if(e.Delta > 0)
            {
                // scroll down
                viewPreviousImage();
            }
            else if (e.Delta < 0)
            {
                // scroll up
                viewNextImage();
            }
        }

        private void viewNextImage()
        { 
            // advance to next image
            currentFile++;
            
            // check if gone too far
            if (currentFile >= files.Count)
            {
                // loop back to beginning
                currentFile = 0;
            }

            // display this file path
            textBox1.Text = files[currentFile];

            // display current file number
            feedbackLabel.Text = Convert.ToString(currentFile + 1) + " of " + files.Count.ToString();

            // display this file in the picturebox
            try
            {
                pictureBox1.Load(files[currentFile]);
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        private void viewPreviousImage()
        { 
            // advance to previous image
            currentFile--;

            // check if gone too far
            if (currentFile < 0)
            {
                // loop forward to end
                currentFile = files.Count - 1;
            }

            // display this file path
            textBox1.Text = files[currentFile];

            // display current file number
            feedbackLabel.Text = Convert.ToString(currentFile + 1) + " of " + files.Count.ToString();

            // display this file in the picturebox
            try
            {
                pictureBox1.Load(files[currentFile]);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
		
    }
}