Code

function doHighlight(bodyText, searchTerm, highlightStartTag, highlightEndTag)
{
  // the highlightStartTag and highlightEndTag parameters are optional
  if ((!highlightStartTag) || (!highlightEndTag)) {
    highlightStartTag = "<font style='color:blue; background-color:yellow;'>";
    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)
{
  alert("I WORK 1 ");
  // 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;
  alert(html1);
  alert(titl);
  for (var i = 0; i < searchArray.length; i++) {
    bodyText = doHighlight(bodyText, searchArray[i], highlightStartTag, highlightEndTag);
  }
  alert("I WORK 1.1 ");
  document.body.innerHTML = bodyText;
  return true;
}

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:blue; background-color:yellow;'>";
    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 = prompt(promptText, defaultText);

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

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




document.addEventListener('DOMContentLoaded', function() {
    var btn_search = document.getElementById('btn_search');
    // onClick's logic below:
    btn_search.addEventListener('click', function() {
        highlightSearchTerms("web",true,true,"<font style='color:blue; background-color:yellow;'>","</font>");
    });
});