Elm:
下载网页

import Browser
import Http
import Html exposing (Html, text, div, button)
import Html.Events exposing (onClick)

type Msg
    = Fetch
    | ReceiveResponse (Result Http.Error String)

type alias Model =
    { content : String
    , error : Maybe String
    }

init : Model
init =
    { content = ""
    , error = Nothing
    }

update : Msg -> Model -> (Model, Cmd Msg)
update msg model =
    case msg of
        Fetch ->
            ( model
            , Http.get
                { url = "https://example.com"
                , expect = Http.expectString ReceiveResponse
                }
            )
        ReceiveResponse (Ok body) ->
            ( { model | content = body, error = Nothing }, Cmd.none )

        ReceiveResponse (Err _) ->
            ( { model | error = Just "Failed to load content." }, Cmd.none )

view : Model -> Html Msg
view model =
    div []
        [ div []
            [ button [ onClick Fetch ] [ text "Load Page Content" ] ]
        , div []
            [ case model.content of
                "" ->
                    case model.error of
                        Just err ->
                            text err

                        Nothing ->
                            text "Content will appear here after fetching."
                content ->
                    text content
            ]
        ]

main =
    Browser.sandbox { init = init, update = update, view = view }