state 更新如何合并到 React 挂钩中？

Question

Will react merge the state updates for hooks too, like it does for setState

    state={count:0}  
  
    increment = () => {
    this.setState({count: this.state.count+1})
    this.setState({count: this.state.count+2})
    }

In Class component, the last setState action will be taken into consideration.Since the state updates are shallow merged .

When you call setState(), React merges the object you provide into the current state.The merging is shallow.

Object.assign(
    {},
    {count: this.state.count+1},
    {count: this.state.count+2}
)

the final result will be state = {count: 2}

In functional component,

const [count,setCount] = useState(0)

const increment = () => {
    setCount(count+1)
    setCount(count+2)
}

The result is same as Class component count = 2 .

Does setCount in useState hook will behave the same as setState ?, Will setCount(count+1) ever execute?

Answer 1

Its not true what you state here:

"In Class component, the last setState action will be taken into consideration. Since the state updates are shallow merged. ".

Same goes for your example with Object.assign .

The "merge" mentioned in React docs is related to merging with current state, for example:

state = { count: 0, name: 'Dennis' }

// Merged with this.state, the 'name' attribute is not removed
this.setState({count: this.state.count+1})

// the state now is { count: 1, name: 'Dennis' }

While same code, won't work with function component, since its different API, as mentioned in the docs, it doesn't merge.

const [state,setState] = useState({ count: 0, name: 'Dennis' })

// NO MERGE, you assign a new object
setState({count: state.count+1})

// the state now is { count: 1 }

Therefore, asking if the "setState call ever execute" is not related to class / function component, its a matter if the set state call is batched or not.

Does setCount in useState hook will behave the same as setState?, Will setCount(count+1) ever execute?

If the calls don't batch, the first call will be executed.

When set state calls are batched? See here .