JS Array diffing with objects that respect duplicates

test.js

var _ = require('underscore');


var a = [{type: 'green'}];
var b = [{type: 'green'},{type: 'green'}];

var onlyInA = a.filter((current) => {
    return b.filter((current_b) => {
        return _.isEqual(current, current_b);
    }).length == 0
});

var onlyInB = b.filter((current) => {
    return a.filter((current_a) => {
        return _.isEqual(current, current_a);
    }).length == 0
});

var diff = onlyInA.concat(onlyInB);

console.log(diff);

//expected [{type:'green'}]