当我将它与 onClick 中的其他 function 一起使用时，useState 不起作用

Question

I created this state:

const [list, insert] = React.useState(["a","b"]);

And I have a button that when I press it, I want it set list as ["a","b","c"]

It works:

<button onClick={() => insert(list.concat(["c"]))}>Insert</button>

But it doesn't:

<button onClick={() => {list.push("c");insert(list)}}>Insert</button>

And I don't know why

Answer 1

NEVER mutate this.state directly, as calling setState() afterward may replace the mutation you made. Treat this.state as if it were immutable.

use spread operation:

this.setState({ myArray: [...this.state.myArray, 'new value'] }) //simple value
this.setState({ myArray: [...this.state.myArray, ...[1,2,3] ] }) //another array

in your case:

insert([...list,'c'])