This error happens because you try to play a game in the web browser directly when running INDEX.HTML.
Modern browsers have a security system that prevents local files from trying to capture information from other sites via AJAX, but you can disable this security (CROSS-ORIGIN).
The tutorial is for the following browsers:
Google Chrome
Opera (Chromium)
Mozilla Firefox
Google Chrome/Opera:
To disable use the following command line:
--allow-file-access-from-files
Create a browser shortcut on the Desktop.
Right-click on it and select Properties.
In the "Destination" box enter the parameter after the second quotation mark with a space and save.
Close any windows of the chosen Chromium that were run before starting.
Mozilla Firefox:
In the browser address bar enter the following command:
about:config
Press [I'll be careful, I promise!] button.Do not change anything on this screen, just what was shown in the tutorial.
In the search field type:
security.fileuri.strict_origin_policy
Double click this item, it will change from "true" to "false".This is done, but you may need to restart the browser.