React.Basic.Hooks

type Component props = Effect (props -> JSX)

A simple type alias to clean up component definitions.

component :: forall props hooks. String -> (props -> Render Unit hooks JSX) -> Component props

Create a component function given a display name and render function. Creating components is effectful because React uses the function instance as the component's "identity" or "type". Components should be created during a bootstrap phase and not within component lifecycles or render functions.

reactComponent :: forall props hooks. Lacks "children" props => Lacks "key" props => Lacks "ref" props => String -> (Record props -> Render Unit hooks JSX) -> Effect (ReactComponent (Record props))

Create a React component given a display name and render function. Creating components is effectful because React uses the function instance as the component's "identity" or "type". Components should be created during a bootstrap phase and not within component lifecycles or render functions. See componentWithChildren if you need to use the children prop.

reactComponentWithChildren :: forall children props hooks. Lacks "key" props => Lacks "ref" props => String -> ({ children :: ReactChildren children | props } -> Render Unit hooks JSX) -> Effect (ReactComponent { children :: ReactChildren children | props })

Create a React component given a display name and render function. This is the same as component but allows the use of the children prop.

reactComponentFromHook :: forall r props hooks. Lacks "children" props => Lacks "key" props => Lacks "ref" props => String -> ({ render :: r -> JSX | props } -> Hook hooks r) -> Effect (ReactComponent { render :: r -> JSX | props })

Convert a hook to a render-prop component. The value returned from the hook will be passed to the render prop, a function from that value to JSX.

This function is useful for consuming a hook within a non-hook component.

data ReactChildren a

reactChildrenToArray :: forall a. ReactChildren a -> Array a

reactChildrenFromArray :: forall a. Array a -> ReactChildren a

memo :: forall props. Effect (ReactComponent props) -> Effect (ReactComponent props)

Prevents a component from re-rendering if its new props are referentially equal to its old props (not value-based equality -- this is due to the underlying React implementation).

useState :: forall state. state -> Hook (UseState state) (state /\ ((state -> state) -> Effect Unit))

useState' :: forall state. state -> Hook (UseState state) (state /\ (state -> Effect Unit))

data UseState :: Type -> Type -> Type

useEffect :: forall deps. Eq deps => deps -> Effect (Effect Unit) -> Hook (UseEffect deps) Unit

Runs the given effect when the component is mounted and any time the given dependencies change. The effect should return its cleanup function. For example, if the effect registers a global event listener, it should return and Effect which removes the listener.

useEffectOnce :: Effect (Effect Unit) -> Hook (UseEffect Unit) Unit

Like useEffect, but the effect is only performed a single time per component instance. Prefer useEffect with a proper dependency list whenever possible!

useEffectAlways :: Effect (Effect Unit) -> Hook (UseEffect Unit) Unit

Like useEffect, but the effect is performed on every render. Prefer useEffect with a proper dependency list whenever possible!

data UseEffect :: Type -> Type -> Type

useLayoutEffect :: forall deps. Eq deps => deps -> Effect (Effect Unit) -> Hook (UseLayoutEffect deps) Unit

Like useEffect, but the effect is performed on every render. Prefer useEffect with a proper dependency list whenever possible!

useLayoutEffectOnce :: Effect (Effect Unit) -> Hook (UseLayoutEffect Unit) Unit

Like useLayoutEffect, but the effect is only performed a single time per component instance. Prefer useLayoutEffect with a proper dependency list whenever possible!

useLayoutEffectAlways :: Effect (Effect Unit) -> Hook (UseLayoutEffect Unit) Unit

Like useLayoutEffect, but the effect is performed on every render. Prefer useLayoutEffect with a proper dependency list whenever possible!

data UseLayoutEffect :: Type -> Type -> Type

newtype Reducer state action

mkReducer :: forall action state. (state -> action -> state) -> Effect (Reducer state action)

Creating reducer functions for React is effectful because React uses the function instance's reference to optimise rendering behavior.

runReducer :: forall action state. Reducer state action -> state -> action -> state

Run a wrapped Reducer function as a normal function (like runFn2). Useful for testing, simulating actions, or building more complicated hooks on top of useReducer

useReducer :: forall action state. state -> Reducer state action -> Hook (UseReducer state action) (state /\ (action -> Effect Unit))

Use mkReducer to construct a reducer function.

data UseReducer :: Type -> Type -> Type -> Type

readRef :: forall a. Ref a -> Effect a

readRefMaybe :: forall a. Ref (Nullable a) -> Effect (Maybe a)

writeRef :: forall a. Ref a -> a -> Effect Unit

useRef :: forall a. a -> Hook (UseRef a) (Ref a)

data UseRef :: Type -> Type -> Type

useContext :: forall a. ReactContext a -> Hook (UseContext a) a

data UseContext :: Type -> Type -> Type

useEqCache :: forall a. Eq a => a -> Hook (UseEqCache a) a

Cache an instance of a value, replacing it when eq returns false.

This is a low-level performance optimization tool. It can be useful for optimizing a component's props for use with memo, where JavaScript instance equality matters.

data UseEqCache :: Type -> Type -> Type

useMemo :: forall a deps. Eq deps => deps -> (Unit -> a) -> Hook (UseMemo deps a) a

Lazily compute a value. The result is cached until the deps change.

data UseMemo :: Type -> Type -> Type -> Type

useDebugValue :: forall a. a -> (a -> String) -> Hook (UseDebugValue a) Unit

Use this hook to display a label for custom hooks in React DevTools

data UseDebugValue :: Type -> Type -> Type

newtype UnsafeReference a

Constructors

• UnsafeReference a

Instances

• Newtype (UnsafeReference a) _
• Eq (UnsafeReference a)

displayName :: forall props. ReactComponent props -> String

Retrieve the Display Name from a ReactComponent. Useful for debugging and improving error messages in logs.

See also: component

Operator alias for Data.Tuple.Tuple (right-associative / precedence 6)

Shorthand for constructing n-tuples as nested pairs. a /\ b /\ c /\ d /\ unit becomes Tuple a (Tuple b (Tuple c (Tuple d unit)))

Operator alias for Data.Tuple.Tuple (right-associative / precedence 6)

Shorthand for constructing n-tuple types as nested pairs. forall a b c d. a /\ b /\ c /\ d /\ Unit becomes forall a b c d. Tuple a (Tuple b (Tuple c (Tuple d Unit)))

data Ref :: Type -> Type

A React Ref, as created by React.createRef

data ReactContext :: Type -> Type

data ReactComponent :: Type -> Type

Represents a traditional React component. Useful for JavaScript interop and FFI. For example:

foreign import ComponentRequiringJSHacks :: ReactComponent { someProp :: String }

See also: element, toReactComponent

data JSX :: Type

Represents rendered React VDOM (the result of calling React.createElement in JavaScript).

JSX is a Monoid:

• append
  • Merge two JSX nodes using React.Fragment.
• mempty
  • The empty node; renders nothing.

Hint: Many useful utility functions already exist for Monoids. For example, guard can be used to conditionally render a subtree of components.

Instances

• Semigroup JSX
• Monoid JSX

provider :: forall a. ReactContext a -> a -> Array JSX -> JSX

Create a provider JSX given a context value and children.

See also: createContext, consumer

keyed :: String -> JSX -> JSX

Apply a React key to a subtree. React-Basic usually hides React's warning about using key props on components in an Array, but keys are still important for any dynamic lists of child components.

See also: React's documentation regarding the special key prop

fragment :: Array JSX -> JSX

Render an Array of children without a wrapping component.

See also: JSX

empty :: JSX

An empty JSX node. This is often useful when you would like to conditionally show something, but you don't want to (or can't) modify the children prop on the parent node.

See also: JSX, Monoid guard

elementKeyed :: forall props. ReactComponent (Record props) -> { key :: String | props } -> JSX

Create a JSX node from a ReactComponent, by providing the props and a key.

See also: ReactComponent, element, React's documentation regarding the special key prop

element :: forall props. ReactComponent (Record props) -> Record props -> JSX

Create a JSX node from a ReactComponent, by providing the props.

See also: ReactComponent, elementKeyed

createContext :: forall a. a -> Effect (ReactContext a)

Create a ReactContext given a default value. Use provider and consumer to provide and consume context values. Alternatively, use contextProvider and contextConsumer directly if a ReactComponent is required for interop.

See also: provider, consumer, React's documentation regarding Context

contextProvider :: forall a. ReactContext a -> ReactComponent { children :: Array JSX, value :: a }

contextConsumer :: forall a. ReactContext a -> ReactComponent { children :: a -> Array JSX }

consumer :: forall a. ReactContext a -> (a -> Array JSX) -> JSX

Create a consumer JSX from a context value to children.

See also: createContext, producer

newtype Render x y a

Render represents the effects allowed within a React component's body, i.e. during "render". This includes hooks and ends with returning JSX (see pure), but does not allow arbitrary side effects.

The x and y type arguments represent the stack of effects that this Render implements, with x being the stack at the start of this Render, and y the stack at the end.

See purescript-indexed-monad to understand how the order of the stack is enforced at the type level.

Instances

• IxFunctor Render
• IxApply Render
• IxApplicative Render
• IxBind Render
• Functor (Render x y)
• (TypeEquals x y) => Apply (Render x y)
• (TypeEquals x y) => Applicative (Render x y)
• (TypeEquals x y) => Bind (Render x y)
• (TypeEquals x y, Semigroup a) => Semigroup (Render x y a)
• (TypeEquals x y, Monoid a) => Monoid (Render x y a)

type Pure a = forall hooks. Render hooks hooks a

Type alias used to lift otherwise pure functionality into the Render type. Not commonly used.

type Hook (newHook :: Type -> Type) a = forall hooks. Render hooks (newHook hooks) a

Type alias for Render representing a hook.

The newHook argument is a type constructor which takes a set of existing effects and generates a type with a new set of effects (produced by this hook) stacked on top.

unsafeRenderEffect :: forall a. Effect a -> Pure a

Promote an arbitrary Effect to a Pure render effect.

This is unsafe because it allows arbitrary effects to be performed during a render, which may cause them to be run many times by React. You should almost always prefer useEffect!

unsafeHook :: forall a newHook. Effect a -> Hook newHook a

Promote an arbitrary Effect to a Hook.

This is unsafe because it allows arbitrary effects to be performed during a render, which may cause them to be run many times by React. This function is primarily for constructing new hooks using the FFI. If you just want to alias a safe hook's effects, prefer coerceHook.

It's also unsafe because the author of the hook type (the newHook type variable used here) MUST contain all relevant types. For example, UseState has a phantom type to track the type of the value contained. useEffect tracks the type used as the deps. useAff tracks both the deps and the resulting response's type. Forgetting to do this allows the consumer to reorder hook effects. If useState didn't track the return type the following extremely unsafe code would be allowed:

React.do
  if xyz then
    _ <- useState 0
    useState Nothing
  else
    s <- useState Nothing
    _ <- useState 0
    pure s
  ...

The same applies to deps in these examples as they use Eq and a reorder would allow React to pass incorrect types into the eq function!

discard :: forall m z y x b a. IxBind m => m x y a -> (a -> m y z b) -> m x z b

Exported for use with qualified-do syntax

coerceHook :: forall a newHook oldHook hooks. Newtype newHook oldHook => Render hooks oldHook a -> Render hooks newHook a

Rename/alias a chain of hooks. Useful for exposing a single "clean" type when creating a hook to improve error messages and hide implementation details, particularly for libraries hiding internal info.

For example, the following alias is technically correct but when inspecting types or error messages the alias is expanded to the full original type and UseAff is never seen:

type UseAff deps a hooks
  = UseEffect deps (UseState (Result a) hooks)

useAff :: ... -> Hook (UseAff deps a) (Result a)
useAff deps aff = React.do
  ...

coerceHook allows the same code to safely export a newtype instead, hiding the internal implementation:

newtype UseAff deps a hooks
  = UseAff (UseEffect deps (UseState (Result a) hooks))

derive instance ntUseAff :: Newtype (UseAff deps a hooks) _

useAff :: ... -> Hook (UseAff deps a) (Result a)
useAff deps aff = coerceHook React.do
  ...

bind :: forall m z y x b a. IxBind m => m x y a -> (a -> m y z b) -> m x z b

Exported for use with qualified-do syntax