document.write('');单引号要匹配,''中是你要显示的内容,里面不能再有'
MM_showHideLayers('l1','','show','l2','','hide')——〉
MM_showHideLayers("l1","","show","l2","","hide")
or
MM_showHideLayers(\'l1\',\'\',\'show\',\'l2\',\'\',\'hide\')都加个转义符号