title: Cannot read property 'length' of undefined react
body: <pre><code>TypeError: Cannot read property 'length' of undefined
  </code></pre>
  <p>That's what the compiler says when I run my react app. What I do need to do with this?</p>
  <pre class="lang-js prettyprint-override"><code>request = (start,end) =&gt; {
     if(this.state.teams.length &lt; 1){
         axios.get(`${ URL }/teams`)
         .then( response =&gt; {
             this.setState({
                 teams:response.data
             })
         })
     }
  
      axios.get(`${ URL }/articles?_start=${start}&amp;_end=${end}`)
      .then( response =&gt; {
          this.setState({
              items:[...this.state.items,...response.data]
          })
      })
  }
  </code></pre>