form.tsx

import React from 'react';

interface Props {
  onAddTodo: (newDescription: string) => void;
}

export const MyForm = (props: Props) => {

  const handleSubmit = (evt) => {
    evt.preventDefault();
    // reset description state
    props.onAddTodo(evt.target.value);
  };

  return (<form onSubmit={handleSubmit}>
    <input type="text" />
    <input type="submit" />
  </form>);
};

// Usage:

<MyForm onAddTodo={
  (newDescription) => {
    // add newDescription as new todo
  }
} />