// ×Ö·û´®²Ù×÷ͨÓú¯Êý;
// extract front part of string prior to searchString;
function getFront(mainStr,searchStr){
 foundOffset = mainStr.indexOf(searchStr);
 if (foundOffset == -1) {
  return '';
 }
 return mainStr.substring(0,foundOffset);
}
// extract back end of string after searchString;
function getEnd(mainStr,searchStr) {
 foundOffset = mainStr.indexOf(searchStr);
 if (foundOffset == -1) {
  return '';
 }
 return mainStr.substring(foundOffset+searchStr.length,mainStr.length);
}
// insert insertString immediately before searchString;
function insertString(mainStr,searchStr,insertStr) {
 var front = getFront(mainStr,searchStr);
 var end = getEnd(mainStr,searchStr);
 if (front != null && end != null) {
  return front + insertStr + searchStr + end;
 }
 return '';
}
// remove deleteString;
function deleteString(mainStr,deleteStr) {
 return replaceString(mainStr,deleteStr,"");
}
// replace searchString with replaceString;
function replaceString(mainStr,searchStr,replaceStr) {
 var front = getFront(mainStr,searchStr);
 var end = getEnd(mainStr,searchStr);
 if (front != null && end != null) {
  return front + replaceStr + end; 
 }
 return '';
}