I am new to TypeScript. I've got a problem with displaying this.state.something inside the render method or assigning it to a variable inside a function.
Have a look at the most important piece of code:
interface State {
playOrPause?: string;
}
class Player extends React.Component {
constructor() {
super();
this.state = {
playOrPause: 'Play'
};
}
render() {
return(
<div>
<button
ref={playPause => this.playPause = playPause}
title={this.state.playOrPause} // in this line I get an error
>
Play
</button>
</div>
);
}
}
The errors says: "[ts] Property 'playOrPause' does not exist on type 'ReadOnly<{}>'.
I tried to declare the playOrPause property to be a type of string and it didn't work. What am I missing here to make it work?
You need to declare that your component is using the State interface, it used by Typescript's Generics.
interface IProps {
}
interface IState {
playOrPause?: string;
}
class Player extends React.Component<IProps, IState> {
// ------------------------------------------^
constructor(props: IProps) {
super(props);
this.state = {
playOrPause: 'Play'
};
}
render() {
return(
<div>
<button
ref={playPause => this.playPause = playPause}
title={this.state.playOrPause} // in this line I get an error
>
Play
</button>
</div>
);
}
}
In case anyone is wondering how to implement it in functional components with hooks ( not in a class):
const [value, setValue] = useState<number>(0);
useState is a generic function, that means that it can accept a type parameter. This type-parameter will tell TypeScript which types are acceptable for this state.
In my case ( working with TypeScript, and the state value was actually a boolean ) I've had the same problem, I've fixed it by passing the state value I wanted to mark as output to String():
import React, { Component } from 'react';
interface ITestProps {
name: string;
}
interface ITestState {
toggle: boolean;
}
class Test extends Component<ITestProps, ITestState> {
constructor(props: ITestProps) {
super(props);
this.state = {
toggle: false,
};
this.onClick = this.onClick.bind(this);
}
onClick() {
this.setState((previousState, props) => ({
toggle: !previousState.toggle,
}));
}
render() {
return (
<div>
Hello, {this.props.name}!
<br />
Toggle state is: {String(this.state.toggle)}
</div>
)
}
}