Javascript errors will occur when the app launches if there is a missing file or missing permission.  There are a few things you can try to see if you can resolve the issue. 

Windows

Javascript errors are generally caused by 2 things, either Antivirus software or lack of admin privileges on a work computer. If you are using a work computer, unless you have full administrative privileges, you will need to use a different device.

STEP 1-

If you have administrative privileges on your computer, disable the antivirus, download the app, install the app and then re-enable the antivirus software.  The antivirus software will quarantine and remove some key files that will prevent the app from launching and working properly.  You may need to delete the app and all its associated files and reinstall it.  You can skip to STEP 2 if you've tried downloading and installing and are still getting the error.  

STEP 2-

There are also a few anti-virus programs that will quarantine these files again on their regular scans, making our app malfunction again, and they will cause a recurrence of the javascript error.  Creating an exception in the antivirus software program so that the file doesn't get scanned or flagged should resolve the issue.  The process will be similar in any program, but here are the instructions for AVG and AVAST:

AVG:  

Open the AVG program.
Open menu Options.
Select Virus Vault.
Select the file that you wish to restore.  
If needed, click Details to display more information about the removed infection.

You're then going to copy this file and create an exception:

Open the AVG user interface and go to Menu ▸ Settings.
Ensure General is selected in the left panel, then click Exceptions ▸ Add Exception.
Add an exception in one of the following ways: Type the file path, folder path, URL, or command prompt line into the text box, then click Add Exception.  (You're going to paste the file you copied from the vault here)

AVAST:

Right-click on the Avast tray icon

select Virus Chest

Find the quarantined file

You will need to restore it, and copy it, and then create an exception.

-Add an Exception: 

 Open the Avast Antivirus user interface and select ☰ Menu ▸ Settings

Ensure the General tab is selected

then click Exceptions

Click the Add Exception button

Add an exception in one of the following ways: Type the file path, folder path, or URL into the text box, then click Add Exception.  (you will paste the file you copied earlier into the box here)

Javascript Errors on Mac

Javascript errors on Mac are usually caused by one of two things:  a work computer (see the notes above) or an improperly located application file.  If the application is installed in any folder other than the application folder, the app will not function and you will get a Javascript error.  

To fix this, you will need to uninstall the app, and then reinstall it in the applications folder.  See Can I install the app on a different drive? for more information.