index.js

import React from 'react';
import ReactDOM from 'react-dom';
import axios from 'axios';

class Reddit extends React.Component
{
  state = {
    posts: [],
    coolthing: []
  }

  componentDidMount()
  {
    axios.get(`https://www.reddit.com/r/dota2.json`)
      .then(res => {
        const posts = res.data.data.children.map(obj=> obj.data);
        this.setState({posts});
      })
  }

  render() {
    const used = [];
  return(
    
    <div>
      {this.state.posts.map(post => (
        <li key={post.id}> {post.preview.images[0].id} </li>
      ))}
    </div> 

    
  )
  }
}

ReactDOM.render(<Reddit/>, document.getElementById('root'));