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试图让 elm 端口工作以维持会话。

在 index.html 中,脚本包含以下监听器:

  window.addEventListener("load", function(event) {
    app.ports.onSessionChange.send(localStorage.session);
  }, false);

localStorage.session看起来像这样(它会一直留在那里,直到我退出):

{"email":"user@fake.com","token":"eyJhbG...","user_id":1,"handle":"me"}

中的定义Ports.elm是:

port onSessionChange : (Value -> msg) -> Sub msg

此端口连接到Main.elm此处(如果我忘记包含以下一些定义,请告诉我):

subscriptions : Model -> Sub Msg
subscriptions model =
    Ports.onSessionChange sessionChange


sessionChange : Json.Decode.Value -> Msg
sessionChange value =
    let
        result =
            Json.Decode.decodeValue sessionDecoder value
    in
        case result of
            Ok sess ->
                SetSession (Just sess)

            Err err ->
                SetSession Nothing

    ...


type alias Session =
    { email : String
    , token : String
    , user_id : Int
    , handle : String
    }

    ...

import Json.Decode as Decode exposing (..)
import Json.Decode.Pipeline as Pipeline exposing (decode, required)

sessionDecoder : Decode.Decoder Session
sessionDecoder =
    Pipeline.decode Session
        |> Pipeline.required "email" Decode.string
        |> Pipeline.required "token" Decode.string
        |> Pipeline.required "user_id" Decode.int
        |> Pipeline.required "handle" Decode.string

    ...

type Msg
    = NoOp
    | SetSession (Maybe Session)

    ...


update msg model =
    case msg of
        SetSession session ->
            case Debug.log "session = " session of
                Just sess ->
                    ({ model | session = sess } , Cmd.none)

                Nothing ->
                    (model, Cmd.none)

Debug.log "session"页面加载时显示Nothing在控制台中,因此 JS 正在与 elm 对​​话,但解码器似乎失败了。有任何想法吗?

4

1 回答 1

1

我已将您的代码插入到一个最小的工作示例中,一切正常。您可能希望localStorage.session从 javascript 部分中记录 的值,以确保它是有效的 JSON 值。

于 2017-11-15T17:56:45.763 回答