ROT13 (Javascript)

[oceanebelle]

Here is an implementation of ROT13, a kind of weak encryption scheme, in javascript.

function encodeROT13(){
		var frm = document.forms[0];
		var strencode;
		var strencoderet;
		var basenum;

		strencode = frm.txtEncode.value;
		strencoderet = "";
		
		for(i = 0; i < strencode.length; i++){
			if( (strencode.charCodeAt(i) >= 97 && strencode.charCodeAt(i) <= 122 ) || 
			(strencode.charCodeAt(i) >= 65 && strencode.charCodeAt(i) <= 90 )) {
				basenum = (strencode.charCodeAt(i) > 90)? 97 : 65;				
				strencoderet += String.fromCharCode( ((strencode.charCodeAt(i) - basenum + 14) % 26 ) + basenum )				
			} else {
				strencoderet += strencode.charAt(i);
			}
		}
		
		frm.txtEncodeRet.value = strencoderet;
		
	}
	
	function decodeROT13(){
		var frm = document.forms[0];
		var strdecode;
		var strdecoderet;
		var basenum;

		strdecode = frm.txtDecode.value;
		strdecoderet = "";
		
		for(i = 0; i < strdecode.length; i++){
			if( (strdecode.charCodeAt(i) >= 97 && strdecode.charCodeAt(i) <= 122 ) || 
			(strdecode.charCodeAt(i) >= 65 && strdecode.charCodeAt(i) <= 90 )) {
				basenum = (strdecode.charCodeAt(i) > 90)? 97 : 65;
				if (((strdecode.charCodeAt(i) - basenum - 13)) % 26  > 0)	{			
					strdecoderet += String.fromCharCode( ((strdecode.charCodeAt(i) - basenum - 14) % 26 ) + basenum )				
				} else {
					strdecoderet += String.fromCharCode( strdecode.charCodeAt(i) + 12 )				
				}
			} else {
				strdecoderet += strdecode.charAt(i);
			}
		}
		
		frm.txtDecodeRet.value = strdecoderet;
	}

I believe that it can be further enhanced to be more efficient. Can anyone give me ideas?