JavaScript custom function implements method to find the longest common substring of two strings

//查找两个字符串的最长公共子串
function findSubStr(s1,s2){
  var S=sstr= "" ,L1=s1.length,L2=s2.length;
  if (L1>L2){ var s3=s1;s1=s2,s2=s3,L1=s2.length;}
  for ( var j=L1;j> 0 ;j--)
    for ( var i= 0 ;i<=L1-j;i++){
      sstr = s1.substr(i,j);
      if (s2.indexOf(sstr)>= 0 ) return sstr;
    }
  return "" ;
}
document .writeln(findSubStr( "aaa3333" , "baa333cc" )); //aa333
document .writeln(findSubStr( "aaaX3333--" , "baa333ccX3333333x" )); //X3333