Using lodash to check whether an array has duplicate values

function hasDuplicates(a) {
  return _.uniq(a).length !== a.length; 
}

var a = [1,2,1,3,4,5];
var b = [1,2,3,4,5,6];

document.write(hasDuplicates(a), ',',hasDuplicates(b));

<script src="http://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.1.0/lodash.min.js"></script>