SwiftUI-compatible framework for building browser apps with WebAssembly
At the moment Tokamak implements a very basic subset of SwiftUI. Its DOM renderer supports a few
view types and modifiers (you can check the current list in the progress
document), and a new HTML
view for constructing arbitrary HTML. The long-term
goal of Tokamak is to implement as much of SwiftUI API as possible and to provide a few more helpful
additions that simplify HTML and CSS interactions.
If there's some SwiftUI API that's missing but you'd like to use it, please review the existing
issues and
PRs to get more details about the current status, or
create a new issue to let us prioritize the
development based on the demand. We also try to make the development of views and modifiers easier
(with the help from the HTML
view, see the example
below), so pull requests are very welcome!
Don't forget to check the "Contributing"
section first.
If you'd like to participate in the growing SwiftWasm community, you're
also very welcome to join our Discord server, or the #webassembly
channel in the SwiftPM Slack.
Example code
Tokamak API attempts to resemble SwiftUI API as much as possible. The main difference is
that you use import TokamakShim
instead of import SwiftUI
in your files. The former makes
your views compatible with Apple platforms, as well as platforms supported by Tokamak (currently
only WebAssembly/WASI with more coming in the future):
import TokamakShim
struct Counter: View {
@State var count: Int
let limit: Int
var body: some View {
if count < limit {
VStack {
Button("Increment") { count += 1 }
Text("\(count)")
}
.onAppear { print("Counter.VStack onAppear") }
.onDisappear { print("Counter.VStack onDisappear") }
} else {
VStack { Text("Limit exceeded") }
}
}
}
struct CounterApp: App {
var body: some Scene {
WindowGroup("Counter Demo") {
Counter(count: 5, limit: 15)
}
}
}
// @main attribute is not supported in SwiftPM apps.
// See https://bugs.swift.org/browse/SR-12683 for more details.
CounterApp.main()
Arbitrary HTML
With the HTML
view you can also render any HTML you want, including inline SVG:
struct SVGCircle: View {
var body: some View {
HTML("svg", ["width": "100", "height": "100"]) {
HTML("circle", [
"cx": "50", "cy": "50", "r": "40",
"stroke": "green", "stroke-width": "4", "fill": "yellow",
])
}
}
}
HTML
doesn't support event listeners, and is declared in the TokamakStaticHTML
module, which TokamakDOM
re-exports. The benefit of HTML
is that you can use it for static rendering in libraries like TokamakVapor and TokamakPublish.
Another option is the DynamicHTML
view provided by the TokamakDOM
module, which has a listeners
property with a corresponding initializer parameter. You can pass closures that can handle onclick
, onmouseover
and other DOM events for you in the listeners
dictionary. Check out MDN docs for the full list.
Arbitrary styles and scripts
While JavaScriptKit
is a great option for occasional interactions with JavaScript,
sometimes you need to inject arbitrary scripts or styles, which can be done through direct
DOM access:
import JavaScriptKit
let document = JSObject.global.document
let script = document.createElement("script")
script.setAttribute("src", "https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.27.0/moment.min.js")
document.head.appendChild(script)
_ = document.head.insertAdjacentHTML("beforeend", #"""
<link
rel="stylesheet"
href="https://cdnjs.cloudflare.com/ajax/libs/semantic-ui/2.4.1/semantic.min.css">
"""#)
This way both Semantic UI styles and moment.js localized date formatting (or any arbitrary style/script/font added that way) are available in your app.
Requirements for app developers
- macOS 11 and Xcode 13.
- Swift 5.4 or later and Ubuntu 18.04 if you'd like to use Linux. Other Linux distributions are currently not supported.
Requirements for app users
Any browser that supports WebAssembly should work, which currently includes:
- Edge 16+
- Firefox 61+
- Chrome 66+
- (Mobile) Safari 12+
Not all of these were tested though, compatibility reports are very welcome!
Getting started
Tokamak relies on carton
as a primary build tool. As a part of these steps
you'll install carton
via Homebrew on macOS (unfortunately you'll have to build
it manually on Linux). Assuming you already have Homebrew installed, you can create a new Tokamak
app by following these steps:
- Install
carton
:
brew install swiftwasm/tap/carton
If you had carton
installed before this, make sure you have version 0.11.0 or greater:
carton --version
- Create a directory for your project and make it current:
mkdir TokamakApp && cd TokamakApp
- Initialize the project from a template with
carton
:
carton init --template tokamak
- Build the project and start the development server,
carton dev
can be kept running during development:
carton dev
- Open http://127.0.0.1:8080/ in your browser to see the app
running. You can edit the app source code in your favorite editor and save it,
carton
will immediately rebuild the app and reload all browser tabs that have the app open.
You can also clone this repository and run carton dev --product TokamakDemo
in its root
directory. This will build the demo app that shows almost all of the currently implemented APIs.
Security
By default, the DOM renderer will escape HTML control characters in Text
views. If you wish
to override this functionality, you can use the _domTextSanitizer
modifier:
Text("<font color='red'>Unsanitized Text</font>")
._domTextSanitizer(Sanitizers.HTML.insecure)
You can also use custom sanitizers; the argument to _domTextSanitizer
is simply a
String -> String
closure. If _domTextSanitizer
is applied to a non-Text
view,
it will apply to all Text
in subviews, unless overridden.
If you use user-generated or otherwise unsafe strings elsewhere, make sure to properly sanitize them yourself.
Troubleshooting
unable to find utility "xctest"
error when building
This error can only happen on macOS, so make sure you have Xcode installed as listed in the requirements. If you do have Xcode installed but still get the error, please refer to this StackOverflow answer.
Syntax highlighting and autocomplete don't work in Xcode
Open Package.swift
of your project that depends on Tokamak with Xcode and build it for macOS.
As Xcode currently doesn't support cross-compilation for non-Apple platforms, your project can't
be indexed if it doesn't build for macOS, even if it isn't fully function on macOS when running.
If you need to exclude some WebAssembly-specific code in your own app that doesn't compile on macOS,
you can rely on #if os(WASI)
compiler directives.
All relevant modules of Tokamak (including TokamakDOM
) should compile on macOS. You may see issues
with TokamakShim
on macOS Catalina, where relevant SwiftUI APIs aren't supported, but replacing
import TokamakShim
with import TokamakDOM
should resolve the issue until you're able to update
to macOS Big Sur.
If you stumble upon code in Tokamak that doesn't build on macOS and prevents syntax highlighting or autocomplete from working in Xcode, please report it as a bug.
Syntax highlighting and autocomplete don't work in VSCode
Make sure you have the SourceKit LSP extension installed. If you don't trust this unofficial release, please follow the manual building and installation guide. Apple currently doesn't provide an official build of the extension on the VSCode Marketplace unfortunately.
Contributing
See CONTRIBUTING.md
for more details.
Code of Conduct
This project adheres to the Contributor Covenant Code of Conduct. By participating, you are expected to uphold this code. Please report unacceptable behavior to [email protected].
Sponsorship
If this library saved you any amount of time or money, please consider sponsoring the work of its maintainers on their sponsorship pages: @carson-katri, @kateinoigakukun, and @MaxDesiatov. While some of the sponsorship tiers give you priority support or even consulting time, any amount is appreciated and helps in maintaining the project.
Maintainers
In alphabetical order: Carson Katri, David Hunt, Ezra Berch, Jed Fox, Max Desiatov, Morten Bek Ditlevsen, Yuta Saito.
Acknowledgments
- Thanks to the Swift community for building one of the best programming languages available!
- Thanks to everyone who developed React with its reconciler/renderer architecture that inspired Tokamak in the first place.
- Thanks to the designers of the SwiftUI API who showed us how to write UI apps in Swift declaratively (arguably even in a better way than React did).
- Thanks to SwiftWebUI for reverse-engineering some of the bits of SwiftUI and kickstarting the front-end Swift ecosystem for the web.
- Thanks to Render, ReSwift, Katana UI and Komponents for inspiration!
SwiftUI is a trademark owned by Apple Inc. Software maintained as a part of the Tokamak project is not affiliated with Apple Inc.
License
Tokamak is available under the Apache 2.0 license. Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the LICENSE file for more info.