Function for converting camelCase and/or PascalCase strings into a string with normal spacing and a function to test it. If you find a case where it doesn't work, please add it to the comments.

fixCamelCase.js

function fixCamelCase( str )
{
    return str.replace( /(?!^)(\S)?([A-Z][a-z])/, ( m, a, b ) => a ? a + " " + b : m )
		      .replace( /(?:^|\s)[a-z]/g, m => m.toUpperCase() )
		      .replace( /(?:[a-z][A-Z]|\D\d)/g, m => m[0] + " " + m[1] );
}

(function()
{
    var tests =
    {
        "HDD": "HDD",
        "GeneralInvestigation": "General Investigation",
        "Fan": "Fan",
        "ExchangeSVCS":	"Exchange SVCS",
        "BlahIT": "Blah IT",
        "OSSystem": "OS System",
        "ioVariance": "Io Variance",
        "TP50": "TP 50",
        "TP:50": "TP: 50",
        "Hello There": "Hello There",
        "hello there": "Hello There",
        "XmlHTTPResponse": "Xml HTTP Response",
        "Hello there": "Hello There"
    };
        
        function runTest( key )
        {
            if ( fixCamelCase(key) != tests[key] )
            {
                console.error( "Failed [", key, "] Result: [", fixCamelCase(key), "] Expected: [", tests[key], "]" );
            }
        }
        
        Object.keys(tests).forEach( key => runTest(key) );
})();