How to make a search highlighting code?

I've got a script below:
*
* This is the function that actually highlights a text string by
* adding HTML tags before and after all occurrences of the search
* term. You can pass your own tags if you'd like, or if the
* highlightStartTag or highlightEndTag parameters are omitted or
* are empty strings then the default <font> tags will be used.
*/
function doHighlight(bodyText, searchTerm, highlightStartTag, highlightEndTag)
{
// the highlightStartTag and highlightEndTag parameters are optional
if ((!highlightStartTag) || (!highlightEndTag)) {
highlightStartTag = "<font style='color:blue; background-color:yellow;' face=arial>";
highlightEndTag = "</font>";
}

// find all occurences of the search term in the given text,
// and add some "highlight" tags to them (we're not using a
// regular expression search, because we want to filter out
// matches that occur within HTML tags and script blocks, so
// we have to do a little extra validation)
var newText = "";
var i = -1;
var lcSearchTerm = searchTerm.toLowerCase();
var lcBodyText = bodyText.toLowerCase();

while (bodyText.length > 0) {
i = lcBodyText.indexOf(lcSearchTerm, i+1);
if (i < 0) {
newText += bodyText;
bodyText = "";
} else {
// skip anything inside an HTML tag
if (bodyText.lastIndexOf(">", i) >= bodyText.lastIndexOf("<", i)) {
// skip anything inside a <script> block
if (lcBodyText.lastIndexOf("/script>", i) >= lcBodyText.lastIndexOf("<script", i)) {
newText += bodyText.substring(0, i) + highlightStartTag + bodyText.substr(i, searchTerm.length) + highlightEndTag;
bodyText = bodyText.substr(i + searchTerm.length);
lcBodyText = bodyText.toLowerCase();
i = -1;
}
}
}
}

return newText;
}

/*
* This is sort of a wrapper function to the doHighlight function.
* It takes the searchText that you pass, optionally splits it into
* separate words, and transforms the text on the current web page.
* Only the "searchText" parameter is required; all other parameters
* are optional and can be omitted.
*/
function highlightSearchTerms(searchText, treatAsPhrase, warnOnFailure, highlightStartTag, highlightEndTag)
{
// if the treatAsPhrase parameter is true, then we should search for
// the entire phrase that was entered; otherwise, we will split the
// search string so that each word is searched for and highlighted
// individually
if (treatAsPhrase) {
searchArray = [searchText];
} else {
searchArray = searchText.split(" ");
}

if (!document.body || typeof(document.body.innerHTML) == "undefined") {
if (warnOnFailure) {
alert("Sorry, for some reason the text of this page is unavailable. Searching will not work.");
}
return false;
}

var bodyText = document.body.innerHTML;
for (var i = 0; i < searchArray.length; i++) {
bodyText = doHighlight(bodyText, searchArray[i], highlightStartTag, highlightEndTag);
}

document.body.innerHTML = bodyText;
return true;
}

/*
* This displays a dialog box that allows a user to enter their own
* search terms to highlight on the page, and then passes the search
* text or phrase to the highlightSearchTerms function. All parameters
* are optional.
*/
function searchPrompt(defaultText, treatAsPhrase, textColor, bgColor)
{

// This function prompts the user for any words that should
// be highlighted on this web page
if (!defaultText) {
defaultText = "";
}

// we can optionally use our own highlight tag values
if ((!textColor) || (!bgColor)) {
highlightStartTag = "";
highlightEndTag = "";
} else {
highlightStartTag = "<font style='color:" + textColor + "; background-color:" + bgColor + ";'>";
highlightEndTag = "</font>";
}

if (treatAsPhrase) {
promptText = "Please enter the phrase you'd like to search for:";
} else {
promptText = "Please enter the words you'd like to search for, separated by spaces:";
}

searchText = filterin.value

if (!searchText) {
alert("No search terms were entered. Exiting function.");
return false;
}

return highlightSearchTerms(searchText, treatAsPhrase, true, highlightStartTag, highlightEndTag);
}
function searchPromptb(defaultText, treatAsPhrase, textColor, bgColor)
{

// This function prompts the user for any words that should
// be highlighted on this web page
if (!defaultText) {
defaultText = "";
}

// we can optionally use our own highlight tag values
if ((!textColor) || (!bgColor)) {
highlightStartTag = "";
highlightEndTag = "";
} else {
highlightStartTag = "<font style='color:" + textColor + "; background-color:" + bgColor + ";'>";
highlightEndTag = "</font>";
}

if (treatAsPhrase) {
promptText = "Please enter the phrase you'd like to search for:";
} else {
promptText = "Please enter the words you'd like to search for, separated by spaces:";
}

searchText = filterinb.value

if (!searchText) {
alert("No search terms were entered. Exiting function.");
return false;
}

return highlightSearchTerms(searchText, treatAsPhrase, true, highlightStartTag, highlightEndTag);
}

/*
* This function takes a referer/referrer string and parses it
* to determine if it contains any search terms. If it does, the
* search terms are passed to the highlightSearchTerms function
* so they can be highlighted on the current page.
*/
function highlightGoogleSearchTerms(referrer)
{
// This function has only been very lightly tested against
// typical Google search URLs. If you wanted the Google search
// terms to be automatically highlighted on a page, you could
// call the function in the onload event of your <body> tag,
// like this:
// <body onload='highlightGoogleSearchTerms(document.referrer);'>

//var referrer = document.referrer;
if (!referrer) {
return false;
}

var queryPrefix = "q=";
var startPos = referrer.toLowerCase().indexOf(queryPrefix);
if ((startPos < 0) || (startPos + queryPrefix.length == referrer.length)) {
return false;
}

var endPos = referrer.indexOf("&", startPos);
if (endPos < 0) {
endPos = referrer.length;
}

var queryString = referrer.substring(startPos + queryPrefix.length, endPos);
// fix the space characters
queryString = queryString.replace(/%20/gi, " ");
queryString = queryString.replace(/\+/gi, " ");
// remove the quotes (if you're really creative, you could search for the
// terms within the quotes as phrases, and everything else as single terms)
queryString = queryString.replace(/%22/gi, "");
queryString = queryString.replace(/\"/gi, "");

return highlightSearchTerms(queryString, false);
}

/*
* This function is just an easy way to test the highlightGoogleSearchTerms
* function.
*/
function testHighlightGoogleSearchTerms()
{
var referrerString = "http://www.google.com/search?q=javascript%20highlight&start=0";
referrerString = prompt("Test the following referrer string:", referrerString);
return highlightGoogleSearchTerms(referrerString);
}

Forum search