In my react and typescript app, I use: onChange={(e) => data.motto = (e.target as any).value}
.
How do I correctly define the typings for the class, so I wouldn't have to hack my way around the type system with any
?
export interface InputProps extends React.HTMLProps<Input> {
...
}
export class Input extends React.Component<InputProps, {}> {
}
If I put target: { value: string };
I get :
ERROR in [default] /react-onsenui.d.ts:87:18
Interface 'InputProps' incorrectly extends interface 'HTMLProps<Input>'.
Types of property 'target' are incompatible.
Type '{ value: string; }' is not assignable to type 'string'.
This question is related to
reactjs
typescript
types
typescript-typings
When using Child Component We check type like this.
Parent Component:
export default () => {
const onChangeHandler = ((e: React.ChangeEvent<HTMLInputElement>): void => {
console.log(e.currentTarget.value)
}
return (
<div>
<Input onChange={onChangeHandler} />
</div>
);
}
Child Component:
type Props = {
onChange: (e: React.ChangeEvent<HTMLInputElement>) => void
}
export Input:React.FC<Props> ({onChange}) => (
<input type="tex" onChange={onChange} />
)
I use something like this:
import { ChangeEvent, useState } from 'react';
export const InputChange = () => {
const [state, setState] = useState({ value: '' });
const handleChange = (event: ChangeEvent<{ value: string }>) => {
setState({ value: event?.currentTarget?.value });
}
return (
<div>
<input onChange={handleChange} />
<p>{state?.value}</p>
</div>
);
}
The target
you tried to add in InputProps
is not the same target
you wanted which is in React.FormEvent
So, the solution I could come up with was, extending the event related types to add your target type, as:
interface MyEventTarget extends EventTarget {
value: string
}
interface MyFormEvent<T> extends React.FormEvent<T> {
target: MyEventTarget
}
interface InputProps extends React.HTMLProps<Input> {
onChange?: React.EventHandler<MyFormEvent<Input>>;
}
Once you have those classes, you can use your input component as
<Input onChange={e => alert(e.target.value)} />
without compile errors. In fact, you can also use the first two interfaces above for your other components.
Thanks @haind
Yes HTMLInputElement
worked for input field
//Example
var elem = e.currentTarget as HTMLInputElement;
elem.setAttribute('my-attribute','my value');
elem.value='5';
This HTMLInputElement
is interface is inherit from HTMLElement
which is inherited from EventTarget
at root level. Therefore we can assert using as
operator to use specific interfaces according to the context like in this case we are using HTMLInputElement
for input field other interfaces can be HTMLButtonElement
, HTMLImageElement
etc.
For more reference you can check other available interface here
lucky i find a solution. you can
import { ChangeEvent } from 'react';
and then write code like:
e:ChangeEvent<HTMLInputElement>
function handle_change(
evt: React.ChangeEvent<HTMLInputElement>
): string {
evt.persist(); // This is needed so you can actually get the currentTarget
const inputValue = evt.currentTarget.value;
return inputValue
}
And make sure you have "lib": ["dom"]
in your tsconfig
.
the correct way to use in TypeScript is
handleChange(e: React.ChangeEvent<HTMLInputElement>) {
// No longer need to cast to any - hooray for react!
this.setState({temperature: e.target.value});
}
render() {
...
<input value={temperature} onChange={this.handleChange} />
...
);
}
Follow the complete class, it's better to understand:
import * as React from "react";
const scaleNames = {
c: 'Celsius',
f: 'Fahrenheit'
};
interface TemperatureState {
temperature: string;
}
interface TemperatureProps {
scale: string;
}
class TemperatureInput extends React.Component<TemperatureProps, TemperatureState> {
constructor(props: TemperatureProps) {
super(props);
this.handleChange = this.handleChange.bind(this);
this.state = {temperature: ''};
}
// handleChange(e: { target: { value: string; }; }) {
// this.setState({temperature: e.target.value});
// }
handleChange(e: React.ChangeEvent<HTMLInputElement>) {
// No longer need to cast to any - hooray for react!
this.setState({temperature: e.target.value});
}
render() {
const temperature = this.state.temperature;
const scale = this.props.scale;
return (
<fieldset>
<legend>Enter temperature in {scaleNames[scale]}:</legend>
<input value={temperature} onChange={this.handleChange} />
</fieldset>
);
}
}
export default TemperatureInput;
Here is a way with ES6 object destructuring, tested with TS 3.3.
This example is for a text input.
name: string = '';
private updateName({ target }: { target: HTMLInputElement }) {
this.name = target.value;
}
as HTMLInputElement
works for me
An alternative that has not been mentioned yet is to type the onChange function instead of the props that it receives. Using React.ChangeEventHandler:
const stateChange: React.ChangeEventHandler<HTMLInputElement> = (event) => {
console.log(event.target.value);
};
This is when you're working with a FileList
Object:
onChange={(event: React.ChangeEvent<HTMLInputElement>): void => {
const fileListObj: FileList | null = event.target.files;
if (Object.keys(fileListObj as Object).length > 3) {
alert('Only three images pleaseeeee :)');
} else {
// Do something
}
return;
}}
Source: Stackoverflow.com