Remove objects in array with duplicate properties

Let's say I got an array like this:

var arr1 = [ 1, 1, 'a', 'a' ];

And I want to remove duplicates, this snippet is awesome:

var deduped = arr1.filter(function (el, i, arr) {
    return arr.indexOf(el) === i;
});

But I got this array, and I want to remove objects that has duplicate properties:

var obj1 = {
  name: "John",
  id: 1
};
var obj2 = {
  name: "Moe",
  id: 1
};
var obj3 = {
  name: "Jane",
  id: 2
};

var arr2 = [obj1, obj2, obj3];

How do I write a function to remove either one of (in this case) obj1 or obj2 since they have the same id?

I do not want to remove both!

JsFiddle

Reference for code snippet

Thanks in advance.

Use Array#filter with thisArg

thisArg, Value to use as this when executing callback.

var obj1 = {
  name: "John",
  id: 1
};
var obj2 = {
  name: "Moe",
  id: 1
};
var obj3 = {
  name: "Jane",
  id: 'toString'
};

var arr2 = [obj1, obj2, obj3];
var filtered = arr2.filter(function(el) {
  if (!this[el.id]) {
    this[el.id] = true;
    return true;
  }
  return false;
}, Object.create(null));
console.log(filtered);

We can add a step to map all object IDs before

var arr2 = [obj1, obj2, obj3];

var ids = arr2.map(function(obj){
    return obj.id;
})

var deduped2 = arr2.filter(function (el, i, arr) {
    return ids.indexOf(el.id) === i;
});

You could use a compact version of checking and assigning to a hash object.

var obj1 = { name: "John", id: 1 },
    obj2 = { name: "Moe", id: 1 },
    obj3 = { name: "Jane", id: 2 },
    arr2 = [obj1, obj2, obj3],
    filtered = arr2.filter(function(a) {
        return !this[a.id] && (this[a.id] = true);
    }, Object.create(null));

console.log(filtered);