I'm building a simple video player component using purescript-halogen
. The component is supposed to show a blank div with only an input button for the user to select a local file which will then act as a source URL for the video element.
I completed a working model in plain javascript and wanted to port it to purescript/halogen. I got the purescript version to compile but the web console gives me an error message Uncaught TypeError: component.initialState is not a function
and points me to this MDN reference .
This would suggest an issue with how I defined my initialState function but it's fairly standard:
component :: forall q i o m. MonadAff m => H.Component q i o m
component =
H.mkComponent
{ initialState
, render
, eval: H.mkEval $ H.defaultEval { handleAction = handleAction }
}
type State =
{ videoUrl :: Maybe String }
initialState :: forall i. i -> State
initialState _ =
{ videoUrl : Nothing
}
Is it possible that the function is called at the wrong time during its lifecycle, hence making it undefined?
The code for the component is hosted on this Github gist . And I've been following this Github issue as reference.
My package.json
:
"private": true,
"devDependencies": {
"parcel": "1.12.3",
"purescript": "^0.14.0",
"spago": "^0.19.1"
},
"scripts": {
"build": "spago build",
"test": "spago test",
"serve": "parcel dev/index.html --open",
"build-prod": "mkdir -p prod && cp dev/index.html prod/ && rm -rf dist && spago bundle-app --to prod/index.js && parcel build prod/index.html"
},
"dependencies": {
"node": "^15.12.0"
}
}
I compiled using purescript v0.14.0
, spago v0.20.0
, node v16.3.0
and tested on Firefox v89.0
in Ubuntu 20.04.2 LTS
.
Seems the bug is from a pesky line in the code:
HH.input
[ ...
, HP.value "Select file"
...]
According to MDN , the value
property of an input element is used to hold the path to the selected files. Therefore, setting it during element creation is not a well defined action.
The final code (which runs as expected) is:
module App.Video (component) where
import DOM.HTML.Indexed.InputAcceptType (InputAcceptType, InputAcceptTypeAtom(..))
import Data.Foldable (traverse_)
import Data.Maybe (Maybe(..))
import Data.MediaType (MediaType(..))
import Data.Traversable (for_)
import Effect.Aff.Class (class MonadAff)
import Halogen as H
import Halogen.HTML as HH
import Halogen.HTML.Events as HE
import Halogen.HTML.Properties as HP
import Prelude (Unit, bind, const, discard, pure, unit, ($), (=<<), (>>=))
import Web.Event.Event as Event
import Web.File.File as File
import Web.File.FileList as FileList
import Web.File.FileReader.Aff as FileReaderAff
import Web.HTML.HTMLInputElement as InputElement
data Action = HandleFileUpload Event.Event
type State =
{ videoUrl :: Maybe String }
component :: forall q i o m. MonadAff m => H.Component q i o m
component =
H.mkComponent
{ initialState
, render
, eval: H.mkEval $ H.defaultEval { handleAction = handleAction }
}
initialState :: forall input. input -> State
initialState inp =
{ videoUrl : Nothing
}
render :: forall m slots. State -> H.ComponentHTML Action slots m
render state =
case state.videoUrl of
Nothing -> blank_player
Just url -> video_player url
supported_formats :: InputAcceptType
supported_formats =
HP.InputAcceptType
[ AcceptMediaType (MediaType "video/mp4")
, AcceptMediaType (MediaType "video/webm")
]
blank_player :: forall w. HH.HTML w Action
blank_player =
HH.div_
[ HH.span_ [HH.text "Choose file to upload"]
, HH.input
[ HP.type_ HP.InputFile
, HP.accept supported_formats
, HE.onChange HandleFileUpload
]
]
video_player :: forall w i. String -> HH.HTML w i
video_player url =
HH.div_ [
HH.video [HP.src url] []
]
handleAction :: forall m slots o. MonadAff m => Action -> H.HalogenM State Action slots o m Unit
handleAction = case _ of
HandleFileUpload ev → do
traverse_ handleFileUpload (InputElement.fromEventTarget =<< Event.target ev)
handleFileUpload :: forall m slots o. MonadAff m => InputElement.HTMLInputElement -> H.HalogenM State Action slots o m Unit
handleFileUpload inputEl = do
H.liftEffect (InputElement.files inputEl) >>= traverse_ \files ->
for_ (FileList.item 0 files) \file → do
video_url ← H.liftAff $ FileReaderAff.readAsDataURL (File.toBlob file)
H.modify_ (const { videoUrl : Just video_url})
pure unit
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