In this document a generic LotusScript function to mimic @ReplaceSubstring is described. This is a JavaScript version of that function. It handles several situations. For example:

replaceSubstring("hellothere", "l", "x") = "hexxothere"
replaceSubstring("this is a string", "is", "x") = "thx x a string"
replaceSubstring("Here is a long string", "", "xxx") = "Here is a long string"
replaceSubstring("Here is a long string", " ", "") = "Hereisalongstring"
' The slash is a literal character, so "\\" is a single slash
replaceSubstring("\\mysubdir\\mydatabase.nsf", "\\", "/") = "/mysubdir/mydatabase.nsf"
' If the string is "literal \s\w characters", it must be represented literally like "literal \\s\\w characters"
replaceSubstring("literal \\s\\w characters", "\\", "\\\\") = "literal \\s\\w characters"
replaceSubstring("Getting rid of unwanted words", "unwanted", "unneeded") = "Getting rid of unneeded words"

Here is the function:

function replaceSubstring(inputString, fromString, toString) {
   // Goes through the inputString and replaces every occurrence of fromString with toString
   var temp = inputString;
   if (fromString == "") {
      return inputString;
   }
   if (toString.indexOf(fromString) == -1) { // If the string being replaced is not a part of the replacement string (normal situation)
      while (temp.indexOf(fromString) != -1) {
         var toTheLeft = temp.substring(0, temp.indexOf(fromString));
         var toTheRight = temp.substring(temp.indexOf(fromString)+fromString.length, temp.length);
         temp = toTheLeft + toString + toTheRight;
      }
   } else { // String being replaced is part of replacement string (like "+" being replaced with "++") - prevent an infinite loop
      var midStrings = new Array("~", "`", "_", "^", "#");
      var midStringLen = 1;
      var midString = "";
      // Find a string that doesn't exist in the inputString to be used
      // as an "inbetween" string
      while (midString == "") {
         for (var i=0; i < midStrings.length; i++) {
            var tempMidString = "";
            for (var j=0; j < midStringLen; j++) { tempMidString += midStrings[i]; }
            if (fromString.indexOf(tempMidString) == -1) {
               midString = tempMidString;
               i = midStrings.length + 1;
            }
         }
      } // Keep on going until we build an "inbetween" string that doesn't exist
      // Now go through and do two replaces - first, replace the "fromString" with the "inbetween" string
      while (temp.indexOf(fromString) != -1) {
         var toTheLeft = temp.substring(0, temp.indexOf(fromString));
         var toTheRight = temp.substring(temp.indexOf(fromString)+fromString.length, temp.length);
         temp = toTheLeft + midString + toTheRight;
      }
      // Next, replace the "inbetween" string with the "toString"
      while (temp.indexOf(midString) != -1) {
         var toTheLeft = temp.substring(0, temp.indexOf(midString));
         var toTheRight = temp.substring(temp.indexOf(midString)+midString.length, temp.length);
         temp = toTheLeft + toString + toTheRight;
      }
   } // Ends the check to see if the string being replaced is part of the replacement string or not
   return temp; // Send the updated string back to the user
} // Ends the "replaceSubstring" function