title: Ionic 2/3: Runtime Error: Property undefined
body: <p>First of all I'm using Ionic 3.x on macOS.</p>
  
  <p>I'm trying to push some data, into an array.</p>
  
  <p>Within the export class I defined it.</p>
  
  <pre><code>export class HomePage {
     tables: any[]
     //...
     addTable(){
  
      let prompt = this.alertCtrl.create({
        title: 'Add Table',
        subTitle: 'Enter the table number',
        inputs: [{
          name: 'tableNumber',
          placeholder: 'Number',
          type: 'number'
        }],
        buttons: [
          {
            text: 'Cancel'
          },
          {
            text: 'Add',
            handler: data =&gt; {
              let table = {
                number: data.tableNumber,
                name: 'occupied'
              }
              alert('Success');
              this.tables.push(table);
            }
          }
        ]
      });
  }
  </code></pre>
  
  <p>When I test the app in Ionic lab and add a table it gives me the error: Runtime Error
  _this.tables is undefined.</p>
  
  <p>The 'Success' alert gets displayed, so the app crashes at this.tables.push(table); , but I don't know why.</p>