title: How to use a callback in a render() of React component
body: <p>I want to use the result of a server method that does a count on a collection to show it in the render method of a react component. I understand that I must do it from the callback function but it doesn't work for me.</p>
  <p>Server Method:</p>
  <pre><code>export const analysis = new ValidatedMethod({
    name: &quot;analysis&quot;,
    validate: new SimpleSchema({
      codigo: {
        type: String
      },
      rta: {
        type: String
      }
    }).validator(),
    run(one) {
      const rta = Respuesta.find({
        codigo: one.codigo,
        rtatexto: one.rta,
        activo: true
      }).count();
      console.log(rta);
      return Number(rta);
    }
  });
  </code></pre>
  <p>Call from client:</p>
  <pre><code>export default class AnalysisFila extends Component {
    constructor(props) {
      super(props);
    }
  
    render() {
      const one = { codigo: this.props.codigo, rta: this.props.opcion };
      const rta = analysis.call(one, (err, res) =&gt; {
        return (
          &lt;Table.Row&gt;
            &lt;Table.Cell&gt; {this.props.opcion} &lt;/Table.Cell&gt;
            &lt;Table.Cell&gt; {res} &lt;/Table.Cell&gt;
          &lt;/Table.Row&gt;
        );
      });
    }
  }
  </code></pre>
  <p>How do I use the value of <em>res</em> in my component's render method?</p>