mirror of
https://github.com/reactjs/react.dev.git
synced 2026-02-27 03:08:06 +00:00
986d97788c
* Don't use experimental syntax unless necessary * Edit another page * Update another page * Unrelated bikeshed on virtual DOM * Please, no *.jsx, we don't recommend it * Update faq-structure.md * Minor updates * Update faq-ajax.md * Update faq-functions.md * Add binding explanation
63 lines
2.0 KiB
Markdown
63 lines
2.0 KiB
Markdown
---
|
|
id: faq-state
|
|
title: Component State
|
|
permalink: docs/faq-state.html
|
|
layout: docs
|
|
category: FAQ
|
|
---
|
|
|
|
### What does setState do?
|
|
|
|
`setState()` schedules an update to a component's `state` object. When state changes, the component responds by re-rendering.
|
|
|
|
### Why is `setState` is giving me the wrong value?
|
|
|
|
Calls to `setState` are asynchronous - don't rely on `this.state` to reflect the new value immediately after calling `setState`. Pass an updater function instead of an object if you need compute values based on the current state (see below for details).
|
|
|
|
Example of code that will not behave as expected:
|
|
|
|
```jsx
|
|
incrementCount() {
|
|
// Note: this will *not* work as intended.
|
|
this.setState({count: this.state.count + 1});
|
|
}
|
|
|
|
handleSomething() {
|
|
// this.state.count is 1, then we do this:
|
|
this.incrementCount();
|
|
this.incrementCount(); // state wasn't updated yet, so this sets 2 not 3
|
|
}
|
|
```
|
|
|
|
See below for how to fix this problem.
|
|
|
|
### How do I update state with values that depend on the current state?
|
|
|
|
Pass a function instead of an object to setState to ensure the call always uses the most updated version of state (see below).
|
|
|
|
### What is the difference between passing an object or a function in setState?
|
|
|
|
Passing an update function allows you to access the current state value inside the updater. Since `setState` calls are batched, this lets you chain updates and ensure they build on top of each other instead of conflicting:
|
|
|
|
```jsx
|
|
incrementCount() {
|
|
this.setState((prevState) => {
|
|
return {count: prevState.count + 1}
|
|
});
|
|
}
|
|
|
|
handleSomething() {
|
|
// this.state.count is 1, then we do this:
|
|
this.incrementCount();
|
|
this.incrementCount(); // count is now 3
|
|
}
|
|
```
|
|
|
|
[Learn more about setState](/docs/react-component.html#setstate)
|
|
|
|
### Should I use a state management library like Redux or MobX?
|
|
|
|
[Maybe.](http://redux.js.org/docs/faq/General.html#general-when-to-use)
|
|
|
|
It's a good idea to get to know React first, before adding in additional libraries. You can build quite complex applications using only React.
|