title: Angular custom filter with multiple dropdown conditions
body: <p>I am trying to filter with multiple dropdowns conditions. I am able to figure out how to filter them one by one. I want them to show all when nothing is chosen, value = "".</p>
  
  <pre><code>&lt;select class="form-control" ng-model="filter.grade"&gt;
    &lt;option ng-repeat="grade in product_grades" value="{{grade}}"&gt;{{grade}}&lt;/option&gt;
  &lt;/select&gt;
  
  &lt;select class="form-control" ng-model="filter.slump"&gt;
    &lt;option ng-repeat="slump in product_slumps" value="{{slump}}"&gt;{{slump}}&lt;/option&gt;
  &lt;/select&gt;
  
  &lt;select class="form-control" ng-model="filter.flow"&gt;
    &lt;option ng-repeat="flow in product_flows" value="{{flow}}"&gt;{{flow}}&lt;/option&gt;
  &lt;/select&gt;
  
  &lt;select class="form-control" ng-model="filter.last_delivered"&gt;
    &lt;option ng-repeat="last_delivered in product_last_delivereds" value="{{last_delivered}}"&gt;{{displayDate(last_delivered)}}&lt;/option&gt;
  &lt;/select&gt;
  
  &lt;tr ng-repeat="job_product in job_products | filter : customFilter"&gt;
  </code></pre>
  
  <p>For one drop down, I use this.</p>
  
  <pre><code>$scope.customFilter = function (data) {
      if (data.Grade === $scope.filter.grade) {
        return true;
      } else if ($scope.filter.grade === '') {
        return true;
      } else {
        return false;
      }
    };
  </code></pre>
  
  <p>But when I use this for multiple dropdowns, it works. </p>
  
  <pre><code>$scope.customFilter = function (data) {
      if (data.Grade === $scope.filter.grade &amp;&amp; 
        data.Slump === $scope.filter.slump &amp;&amp; 
        data.Flow === $scope.filter.flow &amp;&amp; 
        data.LastDlvDate === $scope.filter.last_delivered) {
        return true;
      } else if ($scope.filter.grade === '') {
        return true;
      } else {
        return false;
      }
    };
  </code></pre>
  
  <p>When I choose a drop option now it doesn't show anything.</p>
  
  <p>Here's a plunker:</p>
  
  <p><a href="http://plnkr.co/edit/elwmuqLvhYhIw3rUrEO1?p=preview" rel="nofollow">http://plnkr.co/edit/elwmuqLvhYhIw3rUrEO1?p=preview</a></p>
  
  <p>I am not sure why $filter for the date is not working.</p>
  
  <p>But I want to show concrete A when choosing grade = "1".</p>