Web Highlighter

Web Highlighter

✨A no-runtime dependency lib for highlighting-note & persistence on any website ✨🖍️

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It's from an idea: highlight texts on the website and save the highlighted areas just like what you do in PDFs.

If you have ever visited medium.com, you must know the feature of higlighting notes: users select a text segment and click the 'highlight' button. Then the text will be highlighted with a shining background color. Besides, the highlighted areas will be saved and recovered when you visit it next time. It's like the simple demo bellow.

This is a usefull feature for readers. If you're a developer, you may want your website support it and attract more visitings. If you're a user (like me), you may want a browser-plugin to do this.

For this reason, the repo (web-highlighter) aims to help you implement highlighting-note on any website quickly (e.g. blogs, document viewers, online books and so on). It contains the core abilities for note highlighting and persistence. And you can implement your own product by some easy-to-use APIs. It has been used for our sites in production.


npm i web-highlighter


Only two lines, highlighted when texts are selected.

import Highlighter from 'web-highlighter';
(new Highlighter()).run();

If you need persistence, four lines make it.

import Highlighter from 'web-highlighter';

// 1. initailize
const highlighter = new Highlighter();

// 2. retrieve data from backend, then highlight it on the page
getRemoteData().then(s => highlighter.fromStore(s.startMeta, s.endMeta, s.id, s.text));

// 3. listen for highlight creating, then save to backend
highlighter.on(Highlighter.event.CREATE, ({sources}) => save(sources));

// 4. auto highlight


A more complex example

import Highlighter from 'web-highlighter';

// won't highlight pre&code elements
const highlighter = new Highlighter({
    exceptSelectors: ['pre', 'code']

// add some listeners to handle interaction, such as hover
    .on('selection:hover', ({id}) => {
        // display different bg color when hover
        highlighter.addClass('highlight-wrap-hover', id);
    .on('selection:hover-out', ({id}) => {
        // remove the hover effect when leaving
        highlighter.removeClass('highlight-wrap-hover', id);
    .on('selection:create', ({sources}) => {
        sources = sources.map(hs => ({hs}));
        // save to backend

// retrieve data from store, and display highlights on the website
    // hs is the same data saved by 'store.save(sources)'
    ({hs}) => highlighter.fromStore(hs.startMeta, hs.endMeta, hs.text, hs.id)

// auto-highlight selections

Besides, there is an example in this repo (in example folder). To play with it, you just need ——

Firstly enter the repository and run

npm i

Then start the example

npm start

Finially visit

Another real product built with web-highlighter (for the highlighting area on the left):

product sample


highlighter = new Highlighter([opts])

Create a new highlighter instance.

opts will be merged into the default options (shown bellow).

    $root: document.documentElement,    // root element for addEventlistener / DFS / ...
    exceptSelectors: null,              // if an element matches the selector, it won't be highlighted
    style: {
        className: 'highlight-wrap'     // the classname for wrap element

exceptSelectors needs null or Array<string>. It suports id selectors, class selectors and tag selectors.

For example, to skip h1 and .title elements:

var highlighter = new Highlighter({
    exceptSelectors: ['h1', '.title']


Start auto-highlighting. When the user select a text segement, a highlighting will be added to the text automatically.


It will stop the auto-highlighting.


When you don't want the highlighter anymore, remember to call it first. It will remove some listeners and do some cleanup.


You can pass a Range object to it and then it will be highlighted. You can use window.getSelection().getRangeAt(0) to get a range object or use document.createRange() to create a new range.

Use it as bellow:

const selection = window.getSelection();
if (selection.isCollapsed) {

highlighter.fromStore(start, end, text, id)

Mostly, you use this api to highlight text by the persisted infomation stored from backend.

These four values are from the HighlightSource object. HighlightSource object is a special object created by web-highlighter when highlighted area created. For persistence in backend (database), it's necessary to find a data structure to represent a dom node. This structure is called HighlightSource in web-highlighter.

Four attributes' meanings:


Remove (clean) a highlighted area by it's unique id. The id will be generated by web-highlighter by default. You can also add a hook for your own rule. Hooks doc here.


Remove all highlighted areas belonging to the root.

highlighter.addClass(classname, id)

Add a classname for highlighted areas (wrap elements) by unique id. You can change a highlighted area's style by using this api.

highlighter.removeClass(classname, id)

Remove the classname by unique id. It's highlighter.addClass's inverse operation.


Get all the wrap nodes in a highlighted area. A highlighted area may contain many segments. It will return all the dom nodes wrapping these segements.

If the id is not passed, it will return all the areas' wrap nodes.


If you have a wrap node, it can return the unique highlight id for you.

Event Listener

web-highlighter use listeners to handle the events.


var highlighter = new Highlighter();
highlighter.on(Highlighter.event.CREATE, function (data, inst, e) {
    // ...

The callback function will receive three parameters:

Highlighter.event is EventType type. It contains:

Different event has different data. Attributes below:


name description type
id the highlight id string


name description type
id the highlight id string


name description type
id the highlight id string


no parameter e

name description type
source HighlightSource object Array
type the reason for creating string

source is a HighlightSource object. It is an object created by web-highlighter when highlighted area created. For persistence in backend (database), it's necessary to use a data structure which can be serialized (JSON.stringify()) to represent a dom node in browsers. HighlightSource is the data structure designed for this.

type explains why a highlighted area is be created. Now type has two possible values: from-input and from-store. from-input shows that a highlighted area is created because of user's selection. from-store means it from a storage.


no parameter e

name description type
ids a list of the highlight id Array


It depends on Selection API.


It provides some hooks for you so that the highlighting behaviour can be controlled better by your own.

To learn more about the hooks, read this doc.