Custom Sorts - Objects

    const people = [
      { id: 12, name: 'Billy', dob: '1998-10-05' },
      { id: 123, name: 'Bart', dob: '1993-02-15' },
      { id: 45, name: 'Belinda', dob: '1996-01-31' },
      { id: 67, name: 'Bonnie', dob: '1998-04-09' },
      { id: 89, name: 'Brenda', dob: '1996-07-08' },
      { id: 34, name: 'Bobby', dob: '1994-09-12' },
      { id: 234, name: 'Blake', dob: '2000-01-01' },
    ];
    
    const log = console.log;
    
    log('\n\n built-in sort method');
    log(people.sort());             // [Object object]
    
    log('\n\n sort by name');
    log(people.sort(byName));       // parameter is name of custom sort function
    
    log('\n\n sort by id');
    log(people.sort(byId));         // parameter is name of custom sort function
    
    log('\n\n sort by date');
    log(people.sort(byDate));       // parameter is name of custom sort function
    
    log('\n\n sort by birthday as it occurs during the year');
    log(people.sort(byBirthday));   // parameter is name of custom sort function
    
    function byName(a, b) {
      //alphabetically by name
      if (a.name > b.name) {
        return 1;
      } else if (b.name > a.name) {
        return -1;
      } else {
        return 0;
      }
    }
    
    function byId(a, b) {
      //numerically by id
      return parseInt(a.id) - parseInt(b.id);
    }
    
    function byDate(a, b) {
      //chronologically by year, month, then day
      return new Date(a.dob).valueOf() - new Date(b.dob).valueOf(); //timestamps
    }
    
    function byBirthday(a, b) {
      //by month and then by day
      let d1 = new Date(a.dob); // 1993-02-15T00:00:00Z =>   1993-02-14T20:00:00EST
      let d2 = new Date(b.dob);
      //log(d1.getDate(), d1.getUTCDate(), d1.getMonth(), d1.getUTCMonth());
      if (d1.getUTCMonth() > d2.getUTCMonth()) {
        return 1;
      } else if (d1.getUTCMonth() < d2.getUTCMonth()) {
        return -1;
      } else {
        //same month
        return d1.getUTCDate() - d2.getUTCDate();
      }
    }