Qiita Teams that are logged in
You are not logged in to any team

Log in to Qiita Team
Community
OrganizationAdvent CalendarQiitadon (β)
Service
Qiita JobsQiita ZineQiita Blog
17
Help us understand the problem. What is going on with this article?
@kilo

React.js で setState が undefined

More than 1 year has passed since last update.

備忘録。

TypeScript + React.js で書いていると

TypeError: Cannot read property 'setState' of undefined

とのエラーが出た。

もとの(エラーが出た)コード

interface IState {
    message: string
}

class App extends React.Component<{}, IState, any> {
    constructor(props: {}) {
        super(props)
        this.state = {
            message: "The button has not been clicked yet."
        }
    }

    public render() {
        return (
            <button onClick={ this.onClickButton }/>
            <p>{ this.message }</p>
        )
    }

    private onClickButton() {
        this.message = "The button has been clicked!"
    }
}

対応

2つ方法があるらしい。

1つめ

bindする

constructor() {
    super(props)
    this.state = {
        message: "The button has not been clicked yet."
    }
    this.onClickButton = this.onClickButton.bind(this)
}

参考: Reactで Uncaught TypeError: Cannot read property 'setState' of undefined と怒られる場合の対処法

2つめ

アロー関数にする

private onClickButton = () => {
    this.setState({
        message: "The button has been clicked!"
    })
}

参考: this.setState is undefined (Stack Overflow)

17
Help us understand the problem. What is going on with this article?
Why not register and get more from Qiita?
  1. We will deliver articles that match you
    By following users and tags, you can catch up information on technical fields that you are interested in as a whole
  2. you can read useful information later efficiently
    By "stocking" the articles you like, you can search right away
kilo
大学生。

Comments

No comments
Sign up for free and join this conversation.
Sign Up
If you already have a Qiita account Login
17
Help us understand the problem. What is going on with this article?