Reinstall Javascript on a Mac Computer
1. Understand how the Javascript software code works. Javascript is integrated into your web browser (e.g. Safari or Mozilla Firefox) and is not a stand-alone program. Reinstalling Javascript typically involves reinstalling your entire browser. Thus, it is best to go through several troubleshooting steps to make your current version of Javascript function before reinstalling your browser.
2. Check for system software updates from Apple. Updates to the Javascript technology are delivered to your computer through such updates. Click the Apple icon in the top left-hand corner of the screen and select 'Software Update.' Download all critical updates.

3. Restart your computer. This clears your system cache and can help resolve any Javascript issues you are experiencing. Click the Apple icon in the top left-hand corner of the screen and select 'Restart.'
4. Check that Javascript is enabled in your web browser. Launch Safari and click 'Preferences.' Click the icon for 'Security' and select the checkbox next to 'Enable Javascript.' Close the dialog box and quit Safari. When you launch Safari again, Javascript will be enabled.
5. Delete the Safari system file. Quit Safari and open the Library file in your Home folder. Double-click the 'Preferences' folder. Locate the 'com.apple.safari.plist' file and delete it. Launch Safari again and see if you still experience problems with Javascript. If you do, launch the browser and download the most recent copy of Safari from Apple's website (link in the Resources section). Delete the copy of Safari in your 'Applications' folder and double-click the installation file you just downloaded to reinstall your browser.
Reinstall Javascript on a Windows Computer
6. Remember that Javascript is not a stand-alone piece of software and is integrated directly into your Windows browser (e.g. Google Chrome or Microsoft Internet Explorer). Reinstalling the Javascript software usually requires a reinstallation of your browser. Therefore, it is ideal to troubleshoot your current version of Javascript before reinstalling your browser.
7. Check for system software updates from Microsoft. Important security updates and bug fixes to the Javascript on your computer are installed through such updates. Launch Internet Explorer and go to the Microsoft Windows Update website (link in the Resources section). Download all critical updates suggested by Microsoft.
8. Restart your PC. This will clear the Windows system cache and may assist in resolving any Javascript errors you are encountering. Click the Start menu in the lower left-hand corner of the screen and select 'Restart.'
9. Verify that Javascript is enabled in your Windows web browser. Launch Internet Explorer and click 'Tools' in the top menu. Select 'Internet Options' from the drop down menu. Click 'Security.' Select the 'Internet' zone. Click 'Default Level' and close the dialog box. Refresh your webpage to enable Javascript.
10. Reinstall Internet Explorer (IE). The process for reinstalling the Internet Explorer web browser differs depending on the version of the browser you are using (e.g. 6, 7 or 8) and the version of Windows you are running (e.g. Windows XP or Windows Vista). Follow the reinstallation instructions on Microsoft's support website (link in the Resources section). Typically, the process involves restarting your computer using the Windows installation disks and reinstalling a clean copy of IE on the system level.