MIME-type and Internet Explorer

Does IE need a MIME type (text/javascript, text/css) for everything to work okay?

I checked it and there doesn’t seem to be any problems if it is left out

IE defaults to ‘text/javascript’ if you leave out the MIME type on script tags. So does HTML 5.

If you use the correct JavaScript MIME type of ‘application/javascript’ then your script will not run on IE - A useful way of setting up scripts that must run as JavaScript and not as JScript.

The reason I asked is because HTML5 doesn’t require these but I wondered if there would be a problem with IE if I left them out

That depends if you are using either JavaScript or CSS in the first place. Though technically to be able to associate an ‘external’ CSS style sheet with a (x)html page you do need to have “text/css” for it to validate; as with a ‘style block’ within the HEAD.

Most HTML User Agents are extremely lax and accept all-sorts of nonsense and typically assume default: “CSS” and “JavaScript”, if you use style sheets and scripting respectively.