mithril-hooks
Use hooks with Mithril.
Introduction
Use hook functions from the React Hooks API in Mithril:
useStateuseEffectuseLayoutEffectuseReduceruseRefuseMemouseCallback- and custom hooks
Online demos
- Simple counter with useState
- 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-hooksimport { withHooks, useState /* and other hooks */ } from "mithril-hooks";Example
// Toggle.ts
import m from 'mithril';
import { withHooks, useState } from 'mithril-hooks';
type ToggleProps = {
isOn?: boolean;
};
const Toggle = withHooks(({ isOn }: ToggleProps) => {
const [isOn, setIsOn] = useState<boolean>(isOn);
return m('.toggle', [
m('button',
{
onclick: () => setIsOn(current => !current),
},
'Toggle',
),
m('div', isOn ? 'On' : 'Off'),
]);
});Use the counter:
import { Toggle } from "./Toggle"
m(Toggle, { isOn: true })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.
Custom hooks 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, a dependency list can be passed as second parameter to instruct when it should rerun:
useEffect(
() => {
document.title = `You clicked ${count} times`
},
[count] // Only re-run the effect if count changes
)For the dependency list, 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 useEffect 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.
API
withHooks
Higher order function that returns a component that works with hook functions.
type TAttrs = {};
const MyComponent = withHooks((attrs?: TAttrs) => {
// Use hooks ...
// Return a view:
return m('div', 'My view')
});The longhand version:
type TAttrs = {};
const RenderFn = (attrs?: TAttrs) => {
// Use hooks ...
// Return a view:
return m('div', 'My view')
};
export const HookedComponent = withHooks<TAttrs>(RenderFn);The returned HookedComponent can be called as any Mithril component:
m(HookedComponent, {
// ... attrs
})Options
| Argument | Type | Required | Description |
|---|---|---|---|
renderFunction |
Function | Yes | Function with view logic |
attrs |
Object | No | Attributes to pass to renderFunction |
Signature
const withHooks: <T>(
renderFunction: (attrs: T) => Vnode<T, {}> | Children,
initialAttrs?: T
) => Component<T, {}>;withHooks also receives vnode and children, where vnode includes the hook state. Extended signature:
const withHooks: <T>(
renderFunction: (
attrs: T & { vnode: Vnode<T, MithrilHooks.State>; children: Children },
) => Vnode<T, MithrilHooks.State> | Children,
initialAttrs?: T,
) => Component<T, MithrilHooks.State>;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:
setCount(current => current + 1)A setter function can be called from another hook:
const [inited, setInited] = useState(false)
useEffect(
() => {
setInited(true)
},
[/* empty array: only run at mount */]
)Signature
const useState: <T>(initialValue?: T) => [
T,
(value: T | ((currentValue: T, index: number) => T)) => void
];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
)Signature
const useEffect: (
fn: () => unknown | (() => unknown),
deps?: unknown[],
) => void;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]
)Signature
const useLayoutEffect: (
fn: () => unknown | (() => unknown),
deps?: unknown[],
) => void;useReducer
From the React docs:
An alternative to useState. Accepts a reducer of type
(state, action) => newState, and returns the current state paired with adispatchmethod. (If you’re familiar with Redux, you already know how this works.)
useReduceris usually preferable touseStatewhen 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";
type TState = {
count: number;
};
type TAction = {
type: string;
};
const counterReducer = (state: TState, action: TAction) => {
switch (action.type) {
case 'increment':
return { count: state.count + 1 };
case 'decrement':
return { count: state.count - 1 };
default:
throw new Error(`Unhandled action: ${action}`);
}
};
type CounterAttrs = {
initialCount: number;
};
const CounterFn = (attrs: CounterAttrs) => {
const { initialCount } = attrs;
const initialState = { count: initialCount }
const [countState, dispatch] = useReducer<TState, TAction>(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 Counter = withHooks(CounterFn);
m(Counter, { initialCount: 0 })Signature
const useReducer: <T, A = void>(
reducer: Reducer<T, A>,
initialValue?: T | U,
initFn?: (args: U) => T,
) => [T, (action: A) => void];
type Reducer<T, A> = (state: T, action: A) => T;useRef
The "ref" object is a generic container whose current property is mutable and can hold any value.
const domRef = useRef<HTMLDivElement>(null)
return [
m("div",
{
oncreate: vnode => dom.current = vnode.dom as HTMLDivElement
},
count
)
]To keep track of a value:
import { withHooks, useState, useEffect, useRef } from "mithril-hooks";
const Timer = withHooks(() => {
const [ticks, setTicks] = useState(0)
const intervalRef = useRef<number>()
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"
)
]
});Signature
const useRef: <T>(initialValue?: T) => { current: T };useMemo
Returns a memoized value.
import { withHooks, useMemo } from "mithril-hooks";
const computeExpensiveValue = (count: number): number => {
// some computationally expensive function
return count + Math.random();
};
const Counter = withHooks(({ count, useMemo }) => {
const memoizedValue = useMemo(
() => {
return computeExpensiveValue(count)
},
[count] // only recalculate when count is updated
)
// Render ...
});Signature
const useMemo: <T>(
fn: MemoFn<T>,
deps?: unknown[],
) => T;
type MemoFn<T> = () => T;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.
const someCallback = (): number => {
return Math.random();
};
type TCallback = () => void;
let previousCallback: TCallback;
const Callback = withHooks(() => {
const [someValue, setSomeValue] = useState(0);
const memoizedCallback = useCallback(() => {
return someCallback();
}, [someValue]);
// Render ...
});Signature
const const useCallback: <T>(
fn: MemoFn<T>,
deps?: unknown[],
) => MemoFn<T>;
type MemoFn<T> = () => T;Omitted hooks
These React hooks make little sense with Mithril and are not included:
useContextuseImperativeHandleuseDebugValue
Custom hooks
// useCount.ts
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.ts
import { withHooks } from "mithril-hooks";
import { useCount } from "./useCount";
type CounterAttrs = {
initialCount: number;
};
const Counter = withHooks(({ initialCount }: CounterAttrs) => {
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"
)
])
});
m(Counter, { initialCount: 0 });Children
Child elements can be accessed through the variable children. See mithril-hooks - Child elements.
type CounterAttrs = {
initialCount: number;
children?: Children;
};
const Counter = withHooks(({ initialCount, children }: CounterAttrs) => {
const [count, setCount] = useState(initialCount);
return [
m("div", `Count: ${count}`),
m(
"button",
{
disabled: count === 0,
onclick: () => setCount((c) => c - 1)
},
"Less"
),
m(
"button",
{
onclick: () => setCount((c) => c + 1)
},
"More"
),
children
];
});
const App = {
view: () =>
m(Counter, { initialCount: 1 }, [m("div", "This is a child element")])
};Troubleshooting
TypeError: Cannot read property 'depsIndex' of undefined
Possibly several instances of mithril-hooks are referenced. Prevent this by pointing the transpiler to a single instance.
When using Webpack, add to the config:
resolve: {
// Make sure that libs are included only once
alias: {
'mithril-hooks': path.resolve(baseDir, 'node_modules/mithril-hooks'),
},
},Compatibility
Tested with Mithril 1.1.6 and Mithril 2.x.
Sizes
┌───────────────────────────────────────────┐
│ │
│ Bundle Name: mithril-hooks.module.js │
│ Bundle Size: 5.96 KB │
│ Minified Size: 2.75 KB │
│ Gzipped Size: 1.19 KB │
│ │
└───────────────────────────────────────────┘
┌────────────────────────────────────────┐
│ │
│ Bundle Name: mithril-hooks.umd.js │
│ Bundle Size: 6.95 KB │
│ Minified Size: 2.57 KB │
│ Gzipped Size: 1.24 KB │
│ │
└────────────────────────────────────────┘
┌─────────────────────────────────────┐
│ │
│ Bundle Name: mithril-hooks.cjs │
│ Bundle Size: 6.18 KB │
│ Minified Size: 2.96 KB │
│ Gzipped Size: 1.26 KB │
│ │
└─────────────────────────────────────┘
History
- Initial version: Barney Carroll
- Updated and enhanced by Arthur Clemens with support from Isiah Meadows
License
MIT