Initials field formatting script

I need a simple input field formatting script that formats initials. All characters should be converted to uppercase and should be followed by a . There are 3 edge cases "Th", "Ch", and "Ph" which should remain like that. Only characters A-Za-z and . should be allowed in the field. Spaces should be coverted to dots. var str ="ABCTH"; // This should result in "A.B.C.T.H" var str2 = "[login to view URL]"; // This should result in "[login to view URL]" var str3 = "abcht"; // This should result in "A.B.C.H.T" var str4 = "A.b.ch.t"; // This should result in "A.B.Ch.T." var str5 = "A b ch t"; // This should result in "A.B.Ch.T."