Отсортировать массив

var a = [
 
[{number:'1849',color:'blue'}],
[{number:'1747',color:'blue'}],
[{number:'174',color:'black'}],
[{number:'156',color:'black'},
{number:'138',color:'blue'},
{number:'118',color:'blue'}],
[{number:'194',color:'black'}]
 
]

var a = [
    [{number:'1849',color:'blue'}],
    [{number:'1747',color:'blue'}],
    [{number:'174',color:'black'}],
    [{number:'156',color:'black'},
        {number:'138',color:'blue'},
        {number:'118',color:'blue'}],
    [{number:'194',color:'black'}]
 
];
 
function sortByColor(a) {
    var numbers = [];
    return a.reduce(function (res, current) {
            current.forEach(function (item) {
                if(item.color === 'blue'){
                    numbers.push(item.number);
                }
            });
        return numbers;
    }, 0).join(',');
}
 
alert(sortByColor(a));

var a = [{number:'1849',color:'blue'},
{number:'1747',color:'blue'},
{number:'174',color:'black'},
{number:'156',color:'black'},
{number:'138',color:'blue'},
{number:'118',color:'blue'},
{number:'194',color:'black'}];
 
var b = a.
  filter(function (i) { return i.color == 'blue'; }).
  map(function (i) { return i.number; }).
  join(', ');
 
alert(b);