Filter with Underscore.js

HTML

<textarea id="output"></textarea>

CSS

textarea{width:800px;height:100px}

JavaScript

var array_of_people = [
   {
       "firstName": "Clark",
       "lastName": "Gable",
       "job": "Reporter",
       "roll": 20
   },
   {
       "firstName": "Bruce",
       "lastName": "Willis",
       "job": "Playboy",
       "roll": 30
   },
   {
       "firstName": "James",
       "lastName": "Parker",
       "job": "Reporter",
       "roll": 40
   }
];

var reporters = _.filter(array_of_people, function(p){ return p.roll == "20"; });

document.getElementById('output').value = JSON.stringify(reporters);