<p>Data:</p>

<pre><code>var objArray = [
  { id: 1, name: "name1", tag: "tag1" },
  { id: 2, name: "name2", tag: "tag1" },
  { id: 3, name: "name3", tag: "tag2" },
  { id: 4, name: "name4", tag: "tag1" },
  { id: 5, name: "name5", tag: "tag1" },
  { id: 6, name: "name6", tag: "tag2" }
];</code></pre>

<button>Generate most common tag</button>

<p>Most common tag is: <span class="common"></span></p>

  var objArray = [
  { id: 1, name: "name1", tag: "tag1" },
  { id: 2, name: "name2", tag: "tag1" },
  { id: 3, name: "name3", tag: "tag2" },
  { id: 4, name: "name4", tag: "tag1" },
  { id: 5, name: "name5", tag: "tag1" },
  { id: 6, name: "name6", tag: "tag2" }
];

var tagArray = _.pluck(objArray,'tag'); //create an array of tag values from the object array
var mostCommonTag = _.chain(tagArray).countBy().pairs().max(_.last).head().value(); //find the most commonly occurring tag value

$('button').on('click',function(){
  $('.common').text(mostCommonTag);
});