Compare and diff two array of objects

array_diff.js

//Requires underscores.js

//Verbose:

var a = [{'id':1, 'value':10}, {'id':2, 'value':20}];
var b = [{'id':1, 'value':10}, {'id':4, 'value':40}];

var arr1 = _.pluck(a, "id");
var arr2 = _.pluck(b, "id");
var diff = _.difference(arr1, arr2);
var result = _.filter(a, function(obj) { 
  return diff.indexOf(obj.id) >= 0; 
});

//Concisely:

var diff = _.difference(_.pluck(a, "id"), _.pluck(b, "id"));
var result = _.filter(a, function(obj) { return diff.indexOf(obj.id) >= 0; });


//Outputs
{
  id: 2
  value: 20
}