Typescript input onchange event.target.value

Generally event handlers should use e.currentTarget.value, e.g.:

onChange = (e: React.FormEvent<HTMLInputElement>) => {
    const newValue = e.currentTarget.value;
}

You can read why it so here (Revert "Make SyntheticEvent.target generic, not SyntheticEvent.currentTarget.").

UPD: As mentioned by @roger-gusmao ChangeEvent more suitable for typing form events.

onChange = (e: React.ChangeEvent<HTMLInputElement>)=> {
   const newValue = e.target.value;
}

as HTMLInputElement works for me

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;

You can do the following:

import { ChangeEvent } from 'react';

const onChange = (e: ChangeEvent<HTMLInputElement>)=> {
   const newValue = e.target.value;
}