I am trying to create a custom 404 error for my website. I am testing this out using XAMPP on Windows.
My directory structure is as follows:
error\\4
The ErrorDocument directive, when supplied a local URL path, expects the path to be fully qualified from the DocumentRoot. In your case, this means that the actual path to the ErrorDocument is
ErrorDocument 404 /JinPortfolio/error/404page.html
When you corrected it in your second try, the reason you see that page instead is because http://localhost/error/404page.html doesn't exist, hence the bit about there being a 404 error in locating the error handling document.