main.swift

import JavaScriptKit
import JavaScriptEventLoop

let alert = JSObject.global.alert.function!
let document = JSObject.global.document

var divElement = document.createElement("div")
divElement.innerText = "Hello, world"
_ = document.body.appendChild(divElement)

var buttonElement = document.createElement("button")
buttonElement.innerText = "Alert demo"
buttonElement.onclick = .object(JSClosure { _ in
    alert("Swift is running on browser!")
    return .undefined
})

_ = document.body.appendChild(buttonElement)

private let jsFetch = JSObject.global.fetch.function!
func fetch(_ url: String) -> JSPromise {
    JSPromise(jsFetch(url).object!)!
}

JavaScriptEventLoop.installGlobalExecutor()

struct Response: Decodable {
    let uuid: String
}

var asyncButtonElement = document.createElement("button")
asyncButtonElement.innerText = "Fetch UUID demo"
asyncButtonElement.onclick = .object(JSClosure { _ in
    Task {
        do {
            let response = try await fetch("https://httpbin.org/uuid").value
            let json = try await JSPromise(response.json().object!)!.value
            let parsedResponse = try JSValueDecoder().decode(Response.self, from: json)
            alert(parsedResponse.uuid)
        } catch {
            print(error)
        }
    }

    return .undefined
})

_ = document.body.appendChild(asyncButtonElement)