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/* jshint esnext:true */

​

var ar = [

    '19.07.2015 6:00',

    '19.07.2015 7:00',

    '19.07.2015 8:00',

    '21.07.2015 14:00',

    '21.07.2015 15:00',

    '21.07.2015 16:00',

    '19.07.2015 20:00',

    '19.07.2015 21:00',

    '13.07.2015 6:00',

    '13.07.2015 7:00',

    '13.07.2015 9:00',

    '13.07.2015 10:00',

    '13.07.2015 11:00',

    '13.07.2015 16:00',

    '13.07.2015 17:00',

    '13.07.2015 8:00',

    '13.07.2015 15:00'

];

var res = ar.sort((a,b) => {

    var d1,m1,y1,h1,d2,m2,y2,h2;

    [d1,m1,y1,h1] = a.split(/[ .:]/);

    [d2,m2,y2,h2] = b.split(/[ .:]/);

    return (y1-y2)||(m1-m2)||(d1-d2)||(h1-h2);

}).reduce((s, e) => {

    var date, time, lastDate, timeStart, timeEnd;

    [date, time] = e.split(' ');

    [lastDate, timeStart, timeEnd] = (s[s.length - 1]||'').split(/[- ]+/);

    if (date == lastDate && parseInt(time) - parseInt(timeEnd) == 1) {

        s[s.length - 1] = `${date} ${timeStart} - ${time}`;

    } else s.push(`${date} ${time} - ${time}`);

    return s;

}, []);

console.log(res);