title: Dict lookup in python to javascript
body: <p>Are the following two expressions equivalent?</p>
  
  <pre><code># python
  PLAN_TO_COST_PER_UNIT.get(planType, value_if_empty)
  
  # javascript
  PLAN_TO_COST_PER_UNIT[planType] || value_if_empty;
  </code></pre>
  
  <p>If not, what would be the closest equivalent in javasript to doing the above python dict lookup?</p>