Typescript complains Property does not exist on type 'JSX.IntrinsicElements' when using React.createClass?

Your component must start with a capital letter I instead of small letter i otherwise TypeScript would yell. Changing item to Item should fix it:

var Item = React.createClass({
  render: function() {
    return (<div>hello world</div>)
  }
});

export default class ItemList extends Component<any, any> {
    render() {
        return (<Item />)
    }
}

That is because your item component's name does not start with a capital letter, causing Typescript to complain. Replacing item with Item could solve this problem.

You can declare your custom element type like this:

import * as React from 'react'

declare global {
  namespace JSX {
    interface IntrinsicElements {
      item: React.DetailedHTMLProps<React.HTMLAttributes<HTMLElement>, HTMLElement>;
    }
  }
}