[newtimebigtime]

1.Общие символы двух строк.
2.Разные символы двух строк.

str1="abcdee"
str2="bcefydyy"

str3="123456"
str4="345678"

joint=function(str1, str2){
   var result=""
   str1.replace(/[\s\S]/g, function(symbol){
     var re=new RegExp(symbol)
     if(re.test(str2)&&!re.test(result)) result+=symbol
   })
   return result
}
   
alert("joint: "+joint(str1, str2))
alert("joint: "+joint(str3, str4))

diff=function(str1, str2){
   var result=""
   str1.replace(/[\s\S]/g, function(symbol){
     var re=new RegExp(symbol)
     if(!re.test(str2)&&!re.test(result)) result+=symbol
   })

   str2.replace(/[\s\S]/g, function(symbol){
     var re=new RegExp(symbol)
     if(!re.test(str1)&&!re.test(result)) result+=symbol
   })

   return result
}
 
alert("diff: "+diff(str1, str2))
alert("diff: "+diff(str3, str4))



//>>>> joint: bcde
//>>>> joint: 3456
//>>>> diff: afy
//>>>> diff: 1278