title: Typescript error TS1005: ':' expected. with Object.assign()
body: <p>I have nested <code>Object.assign()</code> in typescript:</p>
  
  <pre><code>(&lt;any&gt;Object).assign({}, state, {
      action.item_id: (&lt;any&gt;Object).assign({}, state[action.item_id], {
          label_value: action.value
      })
  })
  </code></pre>
  
  <p>This yields those errors:</p>
  
  <pre><code>ERROR in ./src/reducers/ItemsReducer.ts
  (2,19): error TS1005: ':' expected.
  
  ERROR in ./src/reducers/ItemsReducer.ts
  (2,26): error TS1005: ',' expected.
  
  ERROR in ./src/reducers/ItemsReducer.ts
  (2,28): error TS1136: Property assignment expected.
  </code></pre>
  
  <p>The weird thing is that the errors vanish if I fix the key e.g.:</p>
  
  <pre><code>(&lt;any&gt;Object).assign({}, state, {
      "fixed_key": (&lt;any&gt;Object).assign({}, state[action.item_id], {
          label_value: action.value
      })
  })
  </code></pre>
  
  <p>This left me clueless, why isn't it ok to call <code>action.item_id</code> at that place when he doesn't complain few characters after?</p>