Forms

Handling forms is central to many web applications. We will build a simple login form to demonstrate.

First, state and event types are needed to keep track of changes to form input:

type State =
  { username :: String
  , password :: String }

data Event
  = SignIn
  | UsernameChange DOMEvent
  | PasswordChange DOMEvent

UsernameChange and PasswordChange events happen every time the inputs change, and receive a DOM Event from purescript-dom. The SignIn event is triggered when the form is submitted.

foldp :: ∀ fx. Event -> State -> EffModel State Event fx
foldp (SignIn) state =
  { state, effects: [ log "sign in" *> pure Nothing ] }
foldp (UsernameChange ev) state =
  { state: state { username = targetValue ev, effects: [] }
foldp (PasswordChange ev) state =
  { state: state { password = targetValue ev, effects: [] }

The raw DOM event is used to get the value of the inputs. Pux provides targetValue which takes a DOMEvent and returns the value of ev.target.value.

The view uses onChange and onSubmit handlers from Pux.DOM.Events to hook application events to DOM events:

view :: State -> HTML Event
view state =
  form ! name "signin" #! onSubmit (const SignIn) $ do
    input ! type' "text" ! value state.username #! onChange UsernameChange
    input ! type' "password" ! value state.password #! onChange PasswordChange
    button ! type' "submit" $ text "Sign In"

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