Get total number of same objects in javascript

You can filter 0 and 1 values with Array.prototype.filter() and check the length of result (ES6 syntax):

var route = [
    { flyFrom: 'CDG', flyTo: 'DUB', return : 0, },
    { flyFrom: 'DUB', flyTo: 'SXF', return : 0, },
    { flyFrom: 'SFX', flyTo: 'CDG', return : 1, }
];

var zeros = route.filter(r => r.return === 0).length;
var ones = route.filter(r => r.return === 1).length;

ES5 analogy:

var zeros = route.filter(function(r) {
    return r.return === 0;
}).length;

Another solution would be to reduce array:

var zeros = route.reduce((a, b) => a + (b.return === 0), 0);

Quick ES 5 solution:

var zeros = 0, ones = 0;

route.forEach(function(entry) {
    if(entry.return == 0) zeros++;
    else if(entry.return == 1) ones++;
});

alert("Zeros: " + zeros + " | Ones: " + ones);

create a json object. then select what child you want. for example:

var jsonObject = data {
route: [
{
flyFrom: "CDG",
flyTo: "DUB",
return: 0,
},
{
flyFrom: "DUB",
flyTo: "SXF",
return: 0,
},
{
flyFrom: "SFX",
flyTo: "CDG",
return: 1,
}]
}

var zeroCount = 0;
var oneCount = 0;
for(var i = 0; i < jsonObject.route.length; i++){
var j = jsonObject.route[i].return;
if(j == 0) zeroCount++;
else oneCount++;
}

This function will return an object with two keys, outbound and inbound, containing the required messages, e.g. "non-stop", "1 stop", etc.:

function countStops(route) { 
   const legs = route.reduce((result, r) => {
        const leg = r['return'] ? 'inbound' : 'outbound';
        result[leg]++;
        return result;
    }, { outbound: 0, inbound: 0 });

    const message = parts => {
        switch (parts) {
            case 1:
                return 'non-stop';
            case 2:
                return '1 stop';
            default:
                return `${parts - 1} stops`;
        }
    };

    return {
        outbound: message(legs.outbound),
        inbound: message(legs.inbound)
    };
}

See fiddle here.

You can iterate over and count the returns in an object with a single loop.

var data = { route: [{ flyFrom: "CDG", flyTo: "DUB", 'return': 0, }, { flyFrom: "DUB", flyTo: "SXF", 'return': 0, }, { flyFrom: "SFX", flyTo: "CDG", 'return': 1 }] },
    count = {};

data.route.forEach(function (a) {
    count[a.return] = (count[a.return] || 0) + 1;
});

Object.keys(count).forEach(function (k) {
    document.getElementById('id' + k).innerHTML = count[k];
});

<p>for the cases where return: 0 appears <span id="id0">0</span> times --- 1 Stop</p>
<p>for the cases where return: 1 appears <span id="id1">0</span> time --- Non-stop</p>