Mithril-hooks: React hooks api for MithrilJs by ArthurClemens

mithril-hooks

Use hooks in Mithril.

Introduction

Use hook functions from the React Hooks API in Mithril:

useState
useEffect
useLayoutEffect
useReducer
useRef
useMemo
useCallback

Online demos

Editable demos using the Flems playground :

• Simplest example
• Simple form handling with useState
• "Building Your Own Hooks" chat API example - this example roughly follows the React documentation on custom hooks
• Custom hooks and useReducer
• Custom hooks to search iTunes with a debounce function

Usage

npm install mithril-hooks

Use in code:

import { withHooks /*, useState and other hooks */ } from "mithril-hooks"

Signature

withHooks(renderFunction, initialProps) => HookedComponent

Argument Type Required Description renderFunction Function Yes Function ("functional component") that will handle hooks initialProps Object No Any variable to pass to renderFunction

The returned HookedComponent can be called as any Mithril component:

m(HookedComponent, {
  // component props
})

renderFunction will receive a combined object of initialProps and component props.

Example

// counter.js

import { withHooks, useState } from "mithril-hooks"

const Counter = ({ title, defaultTitle, initialCount }) => {
  const [count, setCount] = useState(initialCount)
  return [
    m("h2", title || defaultTitle),
    m("div", count),
    m("button", {
      onclick: () => setCount(count + 1)
    }, "More")
  ]
}

export default withHooks(Counter, { defaultTitle: "Counter" })

Use the counter:

// app.js

import Counter from "./Counter"

m(Counter, { initialCount: 0, title: "Hello" })

Hooks and application logic

Hooks can be defined outside of the component, imported from other files. This makes it possible to define utility functions to be shared across the application.

shows how to define and incorporate these hooks.

Rendering rules

With useState

Mithril's redraw is called when the state is initially set, and every time a state changes value.

With other hooks

Hook functions are always called at the first render.

For subsequent renders, an optional second parameter can be passed to define if it should rerun:

useEffect(
  () => {
    document.title = `You clicked ${count} times`
  },
  [count] // Only re-run the effect if count changes
)

mithril-hooks follows the React Hooks API:

• Without a second argument: will run every render (Mithril lifecycle function view ).
• With an empty array: will only run at mount (Mithril lifecycle function oncreate ).
• With an array with variables: will only run whenever one of the variables has changed value (Mithril lifecycle function onupdate ).

Note that effect hooks do not cause a re-render themselves.

Cleaning up

If a hook function returns a function, that function is called at unmount (Mithril lifecycle function onremove ).

useEffect(
  () => {
    const subscription = subscribe()

    // Cleanup function:
    return () => {
      unsubscribe()
    }
  }
)

At cleanup Mithril's redraw is called.

Default hooks

The React Hooks documentation provides excellent usage examples for default hooks. Let us suffice here with shorter descriptions.

useState

Provides the state value and a setter function:

const [count, setCount] = useState(0)

The setter function itself can pass a function - useful when values might otherwise be cached:

setTicks(ticks => ticks + 1)

A setter function can be called from another hook:

const [inited, setInited] = useState(false)

useEffect(
  () => {
    setInited(true)
  },
  [/* empty array: only run at mount */]
)

useEffect

Lets you perform side effects:

useEffect(
  () => {
    const className = "dark-mode"
    const element = window.document.body
    if (darkModeEnabled) {
      element.classList.add(className)
    } else {
      element.classList.remove(className)
    }
  },
  [darkModeEnabled] // Only re-run when value has changed
)

useLayoutEffect

Similar to useEffect , but fires synchronously after all DOM mutations. Use this when calculations must be done on DOM objects.

useLayoutEffect(
  () => {
    setMeasuredHeight(domElement.offsetHeight)
  },
  [screenSize]
)

useReducer

From the React docs :

An alternative to useState. Accepts a reducer of type (state, action) => newState , and returns the current state paired with a dispatch method. (If you’re familiar with Redux, you already know how this works.)

useReducer is usually preferable to useState when you have complex state logic that involves multiple sub-values or when the next state depends on the previous one.

Example:

import { withHooks, useReducer } from "mithril-hooks"

const counterReducer = (state, action) => {
  switch (action.type) {
    case "increment":
      return { count: state.count + 1 }
    case "decrement":
      return { count: state.count - 1 }
    default:
      throw new Error("Unhandled action:", action)
  }
}

const Counter = ({ initialCount }) => {
  const initialState = { count: initialCount }
  const [countState, dispatch] = useReducer(counterReducer, initialState)
  const count = countState.count

  return [
    m("div", count),
    m("button", {
      disabled: count === 0,
      onclick: () => dispatch({ type: "decrement" })
    }, "Less"),
    m("button", {
      onclick: () => dispatch({ type: "increment" })
    }, "More")
  ]
}

const HookedCounter = withHooks(Counter)

m(HookedCounter, { initialCount: 0 })

useRef

The "ref" object is a generic container whose current property is mutable and can hold any value.

const dom = useRef(null)

return [
  m("div",
    {
      oncreate: vnode => dom.current = vnode.dom
    },
    count
  )
]

To keep track of a value:

import { withHooks, useState, useEffect, useRef } from "mithril-hooks"

const Timer = () => {
  const [ticks, setTicks] = useState(0)
  const intervalRef = useRef()
  
  const handleCancelClick = () => {
    clearInterval(intervalRef.current)
    intervalRef.current = undefined
  }

  useEffect(
    () => {
      const intervalId = setInterval(() => {
        setTicks(ticks => ticks + 1)
      }, 1000)
      intervalRef.current = intervalId
      // Cleanup:
      return () => {
        clearInterval(intervalRef.current)
      }
    },
    [/* empty array: only run at mount */]
  )

  return [
    m("span", `Ticks: ${ticks}`),
    m("button", 
      {
        disabled: intervalRef.current === undefined,
        onclick: handleCancelClick
      },
      "Cancel"
    )
  ]
}

const HookedTimer = withHooks(Timer)

useMemo

Returns a memoized value.

import { withHooks, useMemo } from "mithril-hooks"

const Counter = ({ count, useMemo }) => {
  const memoizedValue = useMemo(
    () => {
      return computeExpensiveValue(count)
    },
    [count] // only recalculate when count is updated
  )
  // ...
}

useCallback

Returns a memoized callback.

The function reference is unchanged in next renders (which makes a difference in performance expecially in React), but its return value will not be memoized.

let previousCallback = null

const memoizedCallback = useCallback(
  () => {
    doSomething(a, b)
  },
  [a, b]
)

// Testing for reference equality:
if (previousCallback !== memoizedCallback) {
  // New callback function created
  previousCallback = memoizedCallback
  memoizedCallback()
} else {
  // Callback function is identical to the previous render
}

Omitted hooks

These React hooks make little sense with Mithril and are not included:

useContext
useImperativeHandle
useDebugValue

Custom hooks

// useCount.js
import { useState } from "mithril-hooks"

export const useCount = (initialValue = 0) => {
  const [count, setCount] = useState(initialValue)
  return [
    count,                      // value
    () => setCount(count + 1),  // increment
    () => setCount(count - 1)   // decrement
  ]
}

Then use the custom hook:

// app.js
import { withHooks } from "mithril-hooks"
import { useCount } from "./useCount"

const Counter = ({ initialCount }) => {
  const [count, increment, decrement] = useCount(initialCount)
  return m("div", [
    m("p", 
      `Count: ${count}`
    ),
    m("button", 
      {
        disabled: count === 0,
        onclick: () => decrement()
      },
      "Less"
    ),
    m("button", 
      {
        onclick: () => increment()
      },
      "More"
    )
  ])
}

const HookedCounter = withHooks(Counter)

m(HookedCounter, { initialCount: 0 })

Children

Child elements are accessed through the variable children :

import { withHooks, useState } from "mithril-hooks"

const Counter = ({ initialCount, children }) => {
  const [count, setCount] = useState(initialCount)
  return [
    m("div", count),
    children
  ]
}

const HookedCounter = withHooks(Counter)

m(HookedCounter,
  { initialCount: 1 },
  [
    m("div", "This is a child element")
  ]
)

Compatibility

Tested with Mithril 1.1.6 and Mithril 2.x.

Size

1.5 Kb gzipped

Supported browsers

Output from npx browserslist :

and_chr 71
and_ff 64
and_qq 1.2
and_uc 11.8
android 67
baidu 7.12
chrome 72
chrome 71
edge 18
edge 17
firefox 65
firefox 64
ie 11
ie_mob 11
ios_saf 12.0-12.1
ios_saf 11.3-11.4
op_mini all
op_mob 46
opera 57
safari 12
samsung 8.2

History

• Initial version: Barney Carroll
• Updated and enhanced by Arthur Clemens with support from Isiah Meadows

License

MIT