@require this script and you'll get $URL.encode(str) and $URL.decode(str) available.

$URL.encode(str) returns encodeURIComponent(str) but in encoding=document.characterSet

$URL.decode(str) returns decodeURIComponent(str) but in encoding=document.characterSet

for now, only big5 and gbk are supported for $URL.encode(str). $URL.decode(str) supports all encodings that your browser supports.