title: error TS2339: Property 'forEach' does not exist on type '{}'
body: <p>When I'm trying to compile this typescript with npm it told me this error: <code>"error TS2339: Property 'forEach' does not exist on type '{}'."</code></p>
  
  <p>the code is</p>
  
  <pre><code>export class TestComponent{
      array: yo[];
      check(){
          this.array.map(abc=&gt;{
              abc.prop.forEach(ws=&gt;{
                  console.log(ws)
              })
          });
      }
  }
  </code></pre>
  
  <p>but when I force the execute of the code it works perfectly :\</p>