HLive is a server-side WebSocket based dynamic template-less view layer for Go.



HLive is a server-side WebSocket based dynamic template-less view layer for Go.

HLive is a fantastic tool for creating complex and dynamic browser-based user interfaces for developers who want to keep all the logic in Go.

All the power and data available on the backend with the responsive feel of a pure JavaScript solution.

It's a great use case for admin interfaces and internal company tools.


The first version of the API is under active development. Change is likely. Your feedback is welcome.

Please help the project by building something and giving us your feedback.

Table of contents

Quick Start Tutorial

Step 1: Static Page

Import HLive using the optional alias l:

package main

import l "github.com/SamHennessy/hlive"

Let's create our first page:

func home() *l.Page {
	page := l.NewPage()
	page.Body.Add("Hello, world.")

	return page

Next we use a PageServer to add it to an HTTP router:

func main() {
	http.Handle("/", l.NewPageServer(home))

	log.Println("Listing on :3000")

	if err := http.ListenAndServe(":3000", nil); err != nil {
		log.Println("Error: http listen and serve:", err)

Your editor should add the extra imports http and log for you.

You can now run it, for example:

go run ./tutorial/helloworld/helloworld.go

In a browser go to http://localhost:3000 you should see this:

Hello world step 1

Step 2: Interactive Page

HLive is all about interactive content. We're going to add a text input field to let us type our own hello message.

We need to replace our existing home function. We need a string to hold our message:

func home() *l.Page {
	var message string

Now we're going to create a Component. Component's are HTML tags that can react to browser events. We are going to base our Component on the input HTML tag.

	input := l.C("input")

We want to set the input to a text type. We do this adding aAttrs map to our Component.

	input.Add(l.Attrs{"type": "text"})

Here we add an EventBinding to listen to "keyup" JavaScript events. When triggered, the handler function will be called. Our handler will update message. It does this by using the data in the passed Event parameter.

	input.On(l.On("keyup", func(ctx context.Context, e l.Event) {
		message = e.Value

We create a new Page like before:

	page := l.NewPage()

Here we add our input to the body but first we wrap it in a div tag.

	page.Body.Add(l.T("div", input))

Next, we will display our message. Notice that we're passing message by reference. That's key for making this example work. We'll also add an "hr" tag to stop it being squashed todeather.

	page.Body.Add("Hello, ", &message)

Finally, we return the Page we created.

	return page

Let's see that all together, but this time I'm going to use some shortcuts. Can you spot the differences?

func home() *l.Page {
	var message string

	input := l.C("input",
		l.Attrs{"type": "text"},
		l.OnKeyUp(func(ctx context.Context, e l.Event) {
			message = e.Value

	page := l.NewPage()
		l.T("div", input),
		"Hello, ", &message,

	return page

Run it and type something into the input. The page should update to display what you typed.

Hello world step 2


The examples can be run from the root of the project using go run <path_to_example>. For example:

go run _example/click/click.go




Click a button see a counter update.




Hover over an element and see another element change

Diff Apply


Trigger a Diff Apply event when a DOM change is applied in the browser. Use it to trigger server side logic.




Create a continuously changing animation by chaining Diff Apply callbacks.



Push browser DOM changes from the server without the need for a user to interact with the page.

File Upload


Use a file input to get information about a file before uploading it. Then trigger a file upload from the server when you're ready.

The file is uploaded via WebSocket as a binary (not base64 encoded) object.

Initial Sync


Some browsers, such as FireFox, will not clear data from form fields when the page is reloaded. To the user there is data in the field and if they submit a form they expect that data to be recognised.

Initial sync is a client side process that will send this data to the server after a page refresh. You can check for this behavior in your event handlers.

This example also shows how to get multiple values from inputs that support that.

Local Render


By default, all Components are rendered after each Event Binding that a user triggers.

You can disable this by turning Auto Render off for a component. You can then render that manually but this will rerender the whole page.

If you only want to re-render a single component, and it's children you can do that instead. It's easy to introduce subtle bugs when using this feature.



An example of how to implement a user session using middleware and cookies. It also shows our to pass data from middleware to Components.

Using middleware in HLive is just like any Go app.

To Do List


A simple To Do list app.

URL Parameters


Passing URL params to Components is not straightforward in HLive. Here is an example of how to do it.

This is due to the HLive having a two-step process of loading a page and Components are primarily designed to get data from Events.



A static HTML tag. A Tag has a name (e.g., an <p></p>'s name is hr). A Tag can have zero or more Attributes. A Tag can have child Tags nested inside it. A Tag may be Void, which means it doesn't have a closing tag (e.g., <hr>). Void tags can't have child Tags.


An Attribute has a name and an optional value. (e.g., href="https://example.com" or disabled).

CSS Classes

The HLive implementation of Tag has an optional special way to work with the class attribute.

HLive's CSS is a map[string]bool type. The key is a CSS class, and the value enables the class for rending if true. This allows you to turn a class on and off.

The order of the class names in a single CSS is NOT respected. If the order of class names is significant, you can add them as separate CSS elements, and the order will be respected.

You can add new CSS elements with the same class name, and the original CSS element will be updated. Using this type allows you to turn classes on and off (e.g., show and hide) without growing the Tag's data.

Style Attribute

The HLive implementation of Tag has an optional special way to work with the style attribute.

HLive's Style is a map[string]interface{} type. The key is the CSS rule, and the value is the value of the rule. The value can be a string or nil. If nil, the style rule gets removed.

The order of the style rules in a single Style is NOT respected. If the order of rules is significant, you can add them as separate Style elements, and the order will be respected.

Tag Children

Tag has func GetNodes() *l.NodeGroup. This will return can children a Tag has.

This function is called many times and not always when it's time to render. Calls to GetNodes must be deterministic. If you've not made a change to the Tag the output is expected to be the same.

This function must never get or change data. No calls to a remote API or database.


A Compnent wraps a Tag. It adds the ability to bind events that primarily happens in the browser to itself.


An EventBinding is a combination of an EventType (e.g., click, focus, mouseenter), with a Component and an EventHandler.


The EventHandler is a func(ctx context.Context, e Event) type.

These handlers are where you can fetch data from remote APIs or databases.

Depending on the EventType you'll have data in the Event parameter.


A Node is something that can be rendered into an HTML tag. For example, a string, Tag, or Component. An Attribute is not a Node as it can't be rendered to a complete HTML tag.


An Element is anything associated with a Tag or Component. This means that in addition to nodes, Attribute and EventBinding are also Elements.


A Page is the root element in HLive. There will be a single page instance for a single connected user.

Page has HTML5 boilerplate pre-defined. This boilerplate also includes HLive's JavaScript.

HTML vs WebSocket

When a user requests a page, there are two requests. First is the initial request that generates the pages HTML. Then the second request is to establish a WebSocket connection.

HLive considers the initial HTML generation a throwaway process. We make no assumptions that there will be a WebSocket connection for that exact HTML page.

When an HLive HTML page is loaded in a browser, the HLive JavaScript library will kick into action.

The first thing the JavaScript will do is establish a WebSocket connection to the server. This connection is made using the same URL with ?ws=1 added to the URL. Due to typical load balancing strategies, the server that HLive establishes a Websocket connection to may not be the one that generated the initial HTML.


When the JavaScript establishes the WebSocket connection, the backend will create a new session and send down the session id to the browser.

A PageSession represents a single instance of a Page. There will be a single WebSocket connection to a PageSession.


The PageServer is what handles incoming HTTP requests. It's an http.Handler, so it can be using in your router of choice. When PageServer receives a request, if the request has the ws=1 query parameter, it will start the WebSocket flow. It will create a new instance of your Page. It will then make a new PageSession. Finally, it will pass the request to Page ServerWS function.

If not, then it will create a new Page, generate a complete HTML page render and return that and discard that Page.


It's possible to wrap PageServer in middleware. You can add data to the context like normal. The context will be passed to your Component's Mount function if it has one.


To manage your all the PageSessions PageServer uses a PageSessionStore. By default, each page gets its own PageSessionStore, but it's recommended that you have a single PageSessionStore that's shared by all your Pages.

PageSessionStore can control the number of active PageSessions you have at one time. This control can prevent your servers from becoming overloaded. Once the PageSession limit is reached, PageSessionStore will make incoming WebSocket requests wait for an existing connection to disconnect.

HTTP vs WebSocket Render

Mount is not called on HTTP requests but is called on WebSocket requests.

Tree and Tree Copy

Tree describes a Node and all it's child Nodes.

Tree copy is a critical process that takes your Page's Tree and makes a simplified clone of it. Once done, the only elements in the cloned Tree are Tags and Attributes.

WebSocket Render and Tree Diffing

When it's time to do a WebSocket render, no HTML is rendered (1). What happens is a new Tree Copy is created from the Page. This Tree is compared to the Tree that's in that should be in the browser. The differences are calculated, and instructions are sent to the browser on updating its DOM with our new Tree.

(1) except Attributes, but that's just convenient data format.

First WebSocket Render

When a WebSocket connection is successfully established, we need to do 2 Page renders. The first is to duplicate what should be in the browser. This render will be creating a Tree Copy as if it were going to be rendered to HTML. This Tree is then set as the "current" Tree. Then a WebSocket Tree Copy is made. This copy will contain several attributes not present in the HTML Tree. Also, each Component in the Tree that implements Mounter will be called with the context, meaning the Tree may also have more detail based on any data fetched. This render will then be diffed against the "current" Tree and the diff instructions sent to the browser like normal.

For an initial, successful Page load there will be 3 renders, 2 HTML renders and a WebSocket render.

AutoRender and Manuel Render

By default, HLive's Component will trigger a WebSocket render every time an EventBinding is triggered.

This behaviour can be turned off on Component by setting AutoRender to false.

If you set AutoRender to false you can manually trigger a WebSocket render by calling hlive.RenderWS(ctx context.Context) with the context passed to your handler.

Local Render

If you want only to render a single Component and not the whole page, you can call hlive.RenderComponentWS(ctx context.Context, comp Componenter) you will also want to set any relevant Components to AutoRender false.


TODO: What is it and how does it work


TODO: What is it


HLive's HTML type is a special string type that will render what you've set. One rule is that the HTML in HTML have a single root node.


The goal of HLive is not to require the developer to need to write any JavaScript. As such, we have unique solutions for things like giving fields focus.

Nothing is preventing the developer from adding their JavaScript. If JavaScript changes the DOM in the browser, you could cause HLive's diffing to stop working.

Virtual DOM, Browser DOM

HLive is blind to what the actual state of the browser's DOM is. It assumes that it what it has set it to.



Known Issues

Invalid HTML

If you use invalid HTML typically by using HTML where you should not, the browser will ignore the HTML and not add it to the browsers DOM. If the element were something like a span tag then it may not be perceivable that it's happened. If this happens then the path finding for these tags, and it's children will not work or will work strangely.

We don't have HTML validation rules in HLive, so there is no way of warning you of this being the problem.

Browser Quirks

Browsers are complex things and sometimes act in unexpected ways. For example, if you have a table without a table body tag (tbody) some browsers will add a tbody to the DOM. This breaks HLives element path finding. Another example is that if you have multiple text nodes next to each other, some browsers will combine them.

We'll try and account for this where we can by mimicking the browser's behavior when doing a Tree Copy. We've done this be the text quirk but not the tbody quirk yet.


Phoenix LiveView

For the concept of server-side rendering for dynamic applications.



For it's HTML API.


ReactJS and JSX

For its component approach and template system.


Similar Projects



Live views for GoLang with reactive HTML over WebSockets



Live views and components for golang


API Change


  • Initial sync seems to be triggering when it shouldn't
    • Maybe when the value attribute doesn't exist?
  • Context is already dead when trying calling other services
  • Set the z-index higher than Bulma menu for default disconnect layer
    • Need to test

Internal improvements


  • Add the Grouper interface
    • func GetGroup() []interface{}
    • Add the NoneNodeElementsGroup

Page Pipeline

  • HTTP request w, r


  • Batch message sends and receives in the javascript (https://developer.mozilla.org/en-US/docs/Web/API/HTML_DOM_API/Microtask_guide)
  • If we want to batch sends from the server I think be a problem with out-of-order changes.
  • Add log level to client side logging
  • Send config for debug, and log level down to client side
  • Remove the data- prefix from my attributes?
    • No one else seems to care
  • Event bubbling
    • Prevent bubble in browser
    • Don't bubble events server side
    • Update Docs
  • Add a queue for incoming messages on a page session
    • Maybe multiple concurrent requests is okay, maybe we just batch renders?
  • Use a channel with a single reader to process page events
  • How does it work with grammarly?
  • How does it work with Last Pass?
  • Switch Page.tree to a NodeGroup
  • Get rid of the Page.treeLock by using a channel


  • Add JavaScript test for multi child delete
    • E.g.:
      • d|d|doc|1>1>0>0>1>2||
      • d|d|doc|1>1>0>0>1>3||
  • Page.Close


  • Add initial page sync to concepts
    • An input needs to have binding for this to work
  • Add one page one user to concepts
  • How to debug in browser
  • How on mount render order issues
    • Try to update an element that has already been processed the diff will not be noticed
    • Use the dirty tree error?
  • Logging
  • Plugins
  • Preempt pattern


New Features/Improvements

  • Look for a CSS class to show on a failed reconnect

  • Allow adding mount and unmount function as elements?

  • How well does Alpine.JS work with HLive

  • Can we add a way for a component like List to inform tree copy not to bother doing a diff and just do a full HTML replacement

  • Form

    • Bubble up input and change events?
    • No, no bubble!
  • Cluster

  • Message bus

    • Async
    • Page, server, cluster
    • Plugin based protocol
    • Simple example protocol
      • Websocket?
      • manual node config
    • Prevent race conditions on the page dom
    • Have the page sessions listen to server and cluster messages
  • ComponentList

    • Operations by ID
      • Get by ID
      • Remove By ID
  • User friendly HTTP error pages

    • Display a request ID if it exits
  • Map component ids and event binding ids to a sequential number

    • Would need to map out and in
    • Would provide for smaller ids
    • Could make debugging hard


A highly opinionated web framework that use hot reload and code generation.

  • You install the hhot binary and when in dev mode you get a web UI to create new things, change config etc.
  • Place models in certain folder, and we'll generate the code to wie them up. Same with HLive Pages
  • Use a DI registry to pass config, logger, DB, Cache, etc. to each page.
  • Use off-the-shelf ORM where possible.
  • Form -> Model -> Database flow
  • Data grid
  • Pagination
  • Navigation
  • User management
  • Permissions
  • Batteries included but swappable

HHot Ideas

  • Add the HTTP request to the context by default?
  • Create a middleware package
    • HTTP Request
    • Security
  • Add HTML dsl (Kit?)
  • Cluster
    • User management, who's online
  • Page level data store
    • map[string]interface{}
    • map[string]Adder
    • Available in the context
    • Mutex lock
    • Middleware?
  • Asset management
    • CSS, JS, Font, Images
    • Allow plugins/component libraries to work with this
      • Developer would connect them
    • Mount as a route
    • Use an api to add the JS and CSS to the page HTML
      • Cache busting
    • Watch for change?
      • If change update cache buster
    • Development mode, production mode
  • CSS Build Pipeline
  • Forms
    • Make having forms easy
    • Full form validation
    • Use message bus
  • Form -> Model -> Database flow
  • Automatic TLS via Let’s Encrypt
  • Logging

Older ideas

  • Limit execution by having a worker pool controlled by the page session
    • That way we have a way to limit RAM and CPU

Serializable tree/component state

** Maybe this should just be done with traditional user sessions? **

  • Can we make it so that tree/component state is, serializable?
  • If so we can store it in a database and allow reconnecting later.
  • If load was getting high we can swap sessions in and out of memory
  • We would need a way to capture and store then rehydrate
  • How do we remount event listeners?
    • Need to map state to a function that can rehydrate it
      • Needs to support cold start (we have the data, but we've never seen the component)
    • Maybe we would need to use reflection
      • Only the first time
  • Can't have pointers, outside the components state
  • Maybe all event driven?
  • Encrypt the data by default
  • Could this be a special kind of Page Session?

Do more with the HTTP Server render

  • Think server side render

  • Get the HTTP request easier

  • Easy to cache the response

  • CDN ready

    • Think about what would work well in a CDN
    • Product page
      • Good
        • Pics
        • Description
      • Bad
        • Personal recommendations
        • Recently viewed items

Multi file upload using WS and HTTP

  • Need a count of files
  • Group them together in an event?
  • Make a channel?
  • File upload progress


  • Is a component visible?
  • Trigger event when visible?
  • Scroll events
    • Page position
    • Viewport
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  • Refactor clientside to be golang wasm

    Refactor clientside to be golang wasm

    Nice system.

    you could use the golang websocket lib that supports wasm.

    then your frontend lib could be golang compiled to wasm.


    it’s battle tested and used by some significant projects

    This also means you can share the golang types on the backend and frontend for the platform level types.

    opened by gedw99 3
  • offline


    Make it run 100% in the browser and 100% offline !!

    You can avoid all the network delays by compiling the backend to wasm and run it as a service worker inside the browser.

    Here is a golang example doing that: https://github.com/nlepage/go-wasm-http-server .

    It compiles to WASM with TinyGo.

    Then its all running clientside.

    This can run 100% offline also.

    SO your coding it all in golang, and deploying it all as wasm.

    The Bus between the Service worker and the DOm layer is just replaced with simple message passing.


    You can also add plugins as Web Workers, which are written in golang and compiled to wasm.

    Here is example that compiles to WASM and runs as a Web Worker. https://github.com/henrixapp/pdfcomprezzor

    Debugging is easy:

    Tinygo WASM is very small. You can fully debug this wasm in Chrome easily, because Tinygo exports the DWARF. Here is how to do with with golang: https://blog.noops.land/debugging-webAssembly-from-go-sources-in-chrome-devtools

    Server && SSR

    The websockets can still run inside the Service Worker with no changes except using https://pkg.go.dev/nhooyr.io/websocket, instead of github.com/gorilla/websocket v1.5.0

    You still have all the SSR aspects for Google SEO. The exact same code is running on the server and rendering the HTML page and its DOM.

    If you want you can run the same WASM on the Server using Wazero too. Works well. The Host Function is where you send it out over Websockets or SSE. The same concept applies in the Client as a Service worker, but you're using a different "host Function" to send it to the DOM via Message passing.

    So you can have your cake and eat it to.

    opened by gedw99 1
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