Lý do
Source: https://www.frontendmag.com/tutorials/usereducer-vs-usestate/
Cách bình thường, với useState
function useUndo(initialPresent) {
const [state, setState] = React.useState({
past: [],
present: initialPresent,
future: [],
})
const canUndo = state.past.length !== 0
const canRedo = state.future.length !== 0
const undo = React.useCallback(() => {
setState(currentState => {
const {past, present, future} = currentState
if (past.length === 0) return currentState
const previous = past[past.length - 1]
const newPast = past.slice(0, past.length - 1)
return {
past: newPast,
present: previous,
future: [present, ...future],
}
})
}, [])
const redo = React.useCallback(() => {
setState(currentState => {
const {past, present, future} = currentState
if (future.length === 0) return currentState
const next = future[0]
const newFuture = future.slice(1)
return {
past: [...past, present],
present: next,
future: newFuture,
}
})
}, [])
const set = React.useCallback(newPresent => {
setState(currentState => {
const {present, past} = currentState
if (newPresent === present) return currentState
return {
past: [...past, present],
present: newPresent,
future: [],
}
})
}, [])
const reset = React.useCallback(newPresent => {
setState(() => ({
past: [],
present: newPresent,
future: [],
}))
}, [])
return [state, {set, reset, undo, redo, canUndo, canRedo}]
}
Refactor với useReducer
const UNDO = 'UNDO'
const REDO = 'REDO'
const SET = 'SET'
const RESET = 'RESET'
function undoReducer(state, action) {
const {past, present, future} = state
const {type, newPresent} = action
switch (type) {
case UNDO: {
if (past.length === 0) return state
const previous = past[past.length - 1]
const newPast = past.slice(0, past.length - 1)
return {
past: newPast,
present: previous,
future: [present, ...future],
}
}
case REDO: {
if (future.length === 0) return state
const next = future[0]
const newFuture = future.slice(1)
return {
past: [...past, present],
present: next,
future: newFuture,
}
}
case SET: {
if (newPresent === present) return state
return {
past: [...past, present],
present: newPresent,
future: [],
}
}
case RESET: {
return {
past: [],
present: newPresent,
future: [],
}
}
}
}
function useUndo(initialPresent) {
const [state, dispatch] = React.useReducer(undoReducer, {
past: [],
present: initialPresent,
future: [],
})
const canUndo = state.past.length !== 0
const canRedo = state.future.length !== 0
const undo = React.useCallback(() => dispatch({type: UNDO}), [])
const redo = React.useCallback(() => dispatch({type: REDO}), [])
const set = React.useCallback(
newPresent => dispatch({type: SET, newPresent}),
[],
)
const reset = React.useCallback(
newPresent => dispatch({type: RESET, newPresent}),
[],
)
return [state, {set, reset, undo, redo, canUndo, canRedo}]
}
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