It highlights all words based on selection on whole html page. Im using it for online google apps script editor. its similar function to sublimetext.

Word highliter for programers.js

// ==UserScript==
// @name         Selection highliter
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  It highlights all words based on selection on whole html page. Im using it for online google apps script editor. its similar function to sublimetext.
// @author       [email protected]
// @match        https://script.google.com/macros/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    var style = document.createElement('style');
    style.type = 'text/css';
//    style.innerHTML = '.highiltedSelectedText { background-color: lightgreen; }';
    style.innerHTML = '.highiltedSelectedText { border: 1px solid; }';
    document.getElementsByTagName('head')[0].appendChild(style);

    function highlightWord(word) {
    var xpath = "//text()[contains(., '" + word + "')]";
    var texts = document.evaluate(xpath, document.body, null, XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE, null);
    for (var n = 0; n < texts.snapshotLength; n++) {
        var textNode = texts.snapshotItem(n);
        var p = textNode.parentNode;
        var a = [];
        var frag = document.createDocumentFragment();
        textNode.nodeValue.split(word).forEach(function(text, i) {
            var node;
            if (i) {
                node = document.createElement('span');
//                node.style.backgroundColor = 'lightgreen';
                node.className = "highiltedSelectedText";
                node.appendChild(document.createTextNode(word));
                frag.appendChild(node);
            }
            if (text.length) {
                frag.appendChild(document.createTextNode(text));
            }
            return a;
        });
        p.replaceChild(frag, textNode);
    }
}
    
    document.onclick = function cancelHighlitedText()
    {
        var higlhitedElemts = document.getElementsByClassName("highiltedSelectedText");
        console.log(higlhitedElemts);
        for(var i = 3; i;i--)
        for(var e in higlhitedElemts)
            if((higlhitedElemts[e].className))
                higlhitedElemts[e].className = higlhitedElemts[e].className.replace(/highiltedSelectedText/g,"");
        document.jindraSelectedWord = "";
    };

document.onselect = function() { var selectedText = getSelectionText(); if(selectedText.length <= 3 || document.jindraSelectedWord == selectedText){ return;}  document.jindraSelectedWord = selectedText; console.log("Selection changed: " + selectedText); highlightWord(selectedText); };

    function getSelectionText() {
    var text = "";
    if (window.getSelection) {
        text = window.getSelection().toString();
    } else if (document.selection && document.selection.type != "Control") {
        text = document.selection.createRange().text;
    }
    return text;
}
    
})();