Finding text on html page.

find_text.js

var all = document.getElementsByTagName("*");
var body;
for (var i = 0; i < all.length; i++) {
  if (all[i].tagName === 'BODY') { body = all[i]; break; }
}

function highlightInElement(element, text){
  var elementHtml = element.innerHTML;
  var tags = [];
  var tagLocations= [];
  var htmlTagRegEx = /<{1}\/{0,1}\w+>{1}/;

  //Strip the tags from the elementHtml and keep track of them
  var htmlTag;
  while(htmlTag = elementHtml.match(htmlTagRegEx)){
    tagLocations[tagLocations.length] = elementHtml.search(htmlTagRegEx);
    tags[tags.length] = htmlTag;
    elementHtml = elementHtml.replace(htmlTag, '');
  }

  //Search for the text in the stripped html
  // var textLocation = elementHtml.search(text);
  var textLocations = getIndicesOf(elementHtml, text);

  textLocations.forEach((textLocation) => {
    var highlightHTMLStart = '<span class="edmund-highlight">';
    var highlightHTMLEnd = '</span>';
    elementHtml = elementHtml.replace(text, highlightHTMLStart + text + highlightHTMLEnd);

    //plug back in the HTML tags
    var textEndLocation = textLocation + text.length;
    for(i=tagLocations.length-1; i>=0; i--){
      var location = tagLocations[i];
      if(location > textEndLocation){
          location += highlightHTMLStart.length + highlightHTMLEnd.length;
      } else if(location > textLocation){
          location += highlightHTMLStart.length;
      }
      elementHtml = elementHtml.substring(0,location) + tags[i] + elementHtml.substring(location);
    }
  });
  
  // if(textLocation){
  //     //Add the highlight
  //   var highlightHTMLStart = '<span class="highlight">';
  //   var highlightHTMLEnd = '</span>';
  //   elementHtml = elementHtml.replace(text, highlightHTMLStart + text + highlightHTMLEnd);
  // 
  //   //plug back in the HTML tags
  //   var textEndLocation = textLocation + text.length;
  //   for(i=tagLocations.length-1; i>=0; i--){
  //     var location = tagLocations[i];
  //     if(location > textEndLocation){
  //         location += highlightHTMLStart.length + highlightHTMLEnd.length;
  //     } else if(location > textLocation){
  //         location += highlightHTMLStart.length;
  //     }
  //     elementHtml = elementHtml.substring(0,location) + tags[i] + elementHtml.substring(location);
  //   }
  // }

  //Update the innerHTML of the element
  // return elementHtml;
  element.innerHTML = elementHtml;
}

function getIndicesOf(searchStr, str, caseSensitive) {
    var searchStrLen = searchStr.length;
    if (searchStrLen == 0) {
        return [];
    }
    var startIndex = 0, index, indices = [];
    if (!caseSensitive) {
        str = str.toLowerCase();
        searchStr = searchStr.toLowerCase();
    }
    while ((index = str.indexOf(searchStr, startIndex)) > -1) {
        indices.push(index);
        startIndex = index + searchStrLen;
    }
    return indices;
}