Server-side virtual DOM

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.

• Quick Start Tutorial
  • Step 1: Static Page
  • Step 2: Interactive Page
• Examples
  • Simple
    • Click
    • Hover
    • Diff Apply
  • Advanced
    • Animation
    • Clock
    • File Upload
    • Initial Sync
    • Local Render
    • Session
    • To Do List
    • URL Parameters
• Concepts
  • Tag
  • Attribute
    • CSS Classes
    • Style Attribute
  • Tag Children
  • Components
    • EventBinding
    • EventHandler
  • Node
  • Element
  • Page
    • HTML vs WebSocket
  • PageSession
  • PageServer
  • Middleware
  • PageSessionStore
  • HTTP vs WebSocket Render
  • Tree and Tree Copy
  • WebSocket Render and Tree Diffing
  • First WebSocket Render
  • AutoRender and Manuel Render
  • Local Render
  • Differ
  • Render
  • HTML Type
  • JavaScript
  • Virtual DOM, Browser DOM
  • Lifecycle
• Known Issues
  • Invalid HTML
  • Browser Quirks
• Inspiration
  • Phoenix LiveView
  • gomponents
  • ReactJS and JSX
• Similar Projects
  • GoLive
  • live
• TODO
  • API Change
  • Bugs
  • Internal improvements
    • Groups
    • Page Pipeline
    • Other
  • Tests
  • Docs
  • Security
  • New Features/Improvements
• HHot
  • HHot Ideas
  • Older ideas
    • Serializable tree/component state
    • Do more with the HTTP Server render
    • Multi file upload using WS and HTTP
    • Visibility
• Contributing
  • Run tests
    • Setup
    • Run

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.DOM.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:

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 passed in the Event parameter.

	input.Add(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.DOM.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.DOM.Body.Add(l.T("hr"))
	page.DOM.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()
	page.DOM.Body.Add(
		l.T("div", input),
		l.T("hr"),
		"Hello, ", &message,
	)

	return page
}

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

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

_example/click/click.go

Click a button see a counter update.

_example/hover/hover.go

Hover over an element and see another element change

_example/callback/callback.go

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

_example/animation/animation.go

Create a continuously changing animation by chaining Diff Apply callbacks.

_example/clock/clock.go

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

_example/fileUpload/fileUpload.go

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.

_example/initialSync/initialSync.go

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.

_example/localRender/localRender.go

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.

_example/session/session.go

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.

_example/todo/todo.go

A simple To Do list app.

_example/urlParams/urlParams.go

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 p). 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 a value. (e.g., href="https://example.com" or disabled="").

The HLive implementation of Tag has an optional special way to work with the class attribute. These types are all designed to make toggling CSS classes on and off easy.

HLive's ClassBool 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. (e.g. l.ClassBool{"foo": true, "bar": true, "fizz": true}). The order of the class names in a single ClassBool is NOT respected. If the order of class names is significant, you can add them as separate ClassBool elements, and the order will be respected. You can add a new ClassBool elements with the same class name, and the original ClassBool element will be updated.

Even better is Class, this is a string type that converts into a CSSBool. (e.g. l.Class("foo bar fizz")). The order of the class names is respected. Each class can still be turned off individually using a ClassBool of the ClassOff string type.

ClassList and ClassListOff are string slices that will enable or disable respectively CSS classes. (e.g. l.ClassList{"foo", "bar", "fizz"})

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 style 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 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 should not get or change data. For example, no calls to a remote API or database should happen in this function.

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.

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 is can be though of as the Server Side Rendering phase (SSR). This SSR request will not be used when processing WebSocket requests. This render is a good candidate for use in a CDN.

When an HLive SSR 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 ?hlive=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 SSR Page.

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 used in your router of choice. When PageServer receives a request, if the request has the hlive=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 a SSR 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 on a server.

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.

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

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.

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.

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 an SSR render. 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.

By default, HLive's Component will do a 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.Render(ctx context.Context) with the context passed to your handler.

If you want only to render a single Component and not the whole page, you can call hlive.RenderComponent(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. This is also true in libraries like ReactJS.

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

TODO

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.

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.

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

https://hexdocs.pm/phoenix_live_view/Phoenix.LiveView.html

For it's HTML API.

https://github.com/maragudk/gomponents

For its component approach and template system.

https://reactjs.org/

https://github.com/brendonmatos/golive

Live views for GoLang with reactive HTML over WebSockets

https://github.com/jfyne/live

Live views and components for golang

• Race conditions in examples
• Update docs based on API changes
• Add SSR example

• Add missing data from browser events, like:
  • https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent
  • https://developer.mozilla.org/en-US/docs/Web/API/PointerEvent
  • https://developer.mozilla.org/en-US/docs/Web/API/Touch_events
  • https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent

• Need to reflect in the browser virtual DOM that a select option has become selected when a user selects it
  • So that we can reset the selection (e.g. move dropdowns)
• Can read a POST but can't pass POST data to a render (display errors)
  • Makes Auth logins an issue
  • Workaround it to go a redirect with an url param
• Preempt disable on click prevents form submit in Chrome

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

• HTTP request w, r

• Use binary for websocket

  • Skips UTF8 processing
  • Is this worth the trouble?

• Alternative WebSocket lib?

  • https://github.com/nhooyr/websocket

• Add special logic for class tags

  • Add, remove classes

• Add special logic for style tags

  • Only update property value if needed

• Batch message sends and receives in the javascript (https://developer.mozilla.org/en-US/docs/Web/API/HTML_DOM_API/Microtask_guide)

• Move file upload out of Page.js

• Add log level to client side logging
• Send config for debug, and log level down to client side
  • Set via an attribute

• If that page hash is not found in the cache then we need a fallback
  • Force a browser reload with a new hash?
• Need a way to know that the version of HLive has changed, if so need a hard page reload and cache bypass

• would be a JS binding for reading incoming messages what just blocks when waiting for a message
• another binding sending messages

• 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

• How well does Alpine.JS work with HLive

  • https://dockyard.com/blogs/optimizing-user-experience-with-liveview

• Need a way to test performance improvement ideas
• Why are large tables of data slow to page?
  • It's faster to delete all the rows first
  • 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
  • If we check for hid and they are different, then do an HTML replace

• 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
• Event bubbling
• Prevent default
• Stop propagation
• Explain performance goals
  • Explain why WASM is not a good fit for the goals
• From the beginning tech intro - https://www.reddit.com/r/golang/comments/w5v4oe/comment/ihcm8i9/?utm_source=share&utm_medium=web2x&context=3
• Page hooks

• Add a CSRF token
  • https://github.com/gorilla/csrf
  • Is this needed?

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

  • Set current z-index higher than Bulma menu for default disconnect layer

• Allow adding mount and unmount function as elements?

• Add support for "key" to allow better diff logic for lists

  • Use hid

• Add a func() *l.NodeGroup value

  • Reduce code count
  • Does it solve any real issues

• ComponentList

  • Operations by ID
    • Get by ID
    • Remove By ID

• User friendly HTTP error pages

  • Display a request ID if it exits

• Add can take a func() string this would be kept in the tree and re-run on each render

  • Could be expensive

• 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

Contributions welcome

Install Play wright Go

make install-test

or

go run github.com/playwright-community/playwright-go/cmd/playwright install --with-deps

go test ./...