Category: quickie

I’ve been using Javascript for 2 years now and can not remember ever having to sort collections. 95% of what I am doing is backend services work and I try to off load as much data manipulation to the databases, but this week I have had 7 instances of having to sort data.

This caught me out:

For a given collection:

const collection = [ {name: "Dave"}, {name: "Donna"}, {name: "dave"}, {name: "Derek"}, {name: "Dave"},];

Sorted with:

collection.sort(
  (a,b) => { 
    if (a.name < b.name) return -1; 
    if (a.name > b.name) return 1; 
    return 0;
  })

Returns this:

[ { name: 'Dave' },  { name: 'Dave' },  { name: 'Derek' },  { name: 'Donna' },  { name: 'dave' } ]

Which is not what I need.

.localCompare to the rescue

collection.sort(
  (a, b) => a.name.localeCompare(b.name)
)

Returns this:

[ { name: 'dave' },  { name: 'Dave' },  { name: 'Dave' },  { name: 'Derek' },  { name: 'Donna' } ] 

But there is more

.localCompare method has additional options. For the same collection above, this

collection.sort(
  (a, b) => a.name.localeCompare(b.name, 'en', { sensitivity: 'base' })
)

Returns this:

[ { name: 'Dave' },  { name: 'Dave' },  { name: 'dave' },  { name: 'Derek' },  { name: 'Donna' } ] 

Be aware that full implementation of .localCompare in Node.js is dependant on the version you are running.

The problem is:

Take a date object, set the time to 09:15 the following day. If that day is a Saturday, Sunday or Monday bump the date to the next Tuesday.

Solution:

const reminderTime = (date: Date): Date => {
  const response = new Date(date);
  
  const SUNDAY = 0;
  const MONDAY = 1;
  const TUESDAY = 2;
  const SATURDAY = 6;
  
  response.setDate(response.getDate() + 1);
  
  if ([SUNDAY, MONDAY, SATURDAY].some((x) => x === response.getDay())) {
    response.setDate(response.getDate() + ((TUESDAY + 7 - response.getDay()) % 7));
  }

  response.setHours(9);
  response.setMinutes(15);

  return response;
};

Is the date local or UTC? That depends on how the Date object passed into the method was created. In either case local or UTC is preserved.

Here are some proofs:

console.log(reminderTime(new Date(2020, 10, 2))); 
// Returns Tue Nov 03 2020 09:15:00 GMT+0000 (Greenwich Mean Time) 

console.log(reminderTime(new Date(2020, 10, 3)));
// Returns Wed Nov 04 2020 09:15:00 GMT+0000 (Greenwich Mean Time)

console.log(reminderTime(new Date(2020, 10, 4))); 
// Returns Thu Nov 05 2020 09:15:00 GMT+0000 (Greenwich Mean Time) 

console.log(reminderTime(new Date(2020, 10, 5)));
// Returns Fri Nov 06 2020 09:15:00 GMT+0000 (Greenwich Mean Time) 

console.log(reminderTime(new Date(2020, 10, 6)));
// Returns Tue Nov 10 2020 09:15:00 GMT+0000 (Greenwich Mean Time) 

console.log(reminderTime(new Date(2020, 10, 7)));
// Returns Tue Nov 10 2020 09:15:00 GMT+0000 (Greenwich Mean Time) 

console.log(reminderTime(new Date(2020, 10, 8)));
// Returns Tue Nov 10 2020 09:15:00 GMT+0000 (Greenwich Mean Time) 

console.log(reminderTime(new Date(2020, 10, 9)));
// Returns Tue Nov 10 2020 09:15:00 GMT+0000 (Greenwich Mean Time) 

console.log(reminderTime(new Date(2020, 11, 31)));
// Returns Fri Jan 01 2021 09:15:00 GMT+0000 (Greenwich Mean Time) 

console.log(reminderTime(new Date(2020, 1, 29)));
// Returns Tue Mar 03 2020 09:15:00 GMT+0000 (Greenwich Mean Time) 

console.log(reminderTime(new Date(2020, 1, 30)));
// Returns Tue Mar 03 2020 09:15:00 GMT+0000 (Greenwich Mean Time) 

Solution: (Typescript)

(range as Date[]).sort((a, b) => a.valueOf() - b.valueOf());

My first thought was why not just:

(range as Date[]).sort()

But that does not work. Have a look at the MDN documents and you will see the comparison is done with character’s Unicode code.

Try this in your browsers console to see the solution working

const range = [
  new Date("2020-09-10"),
  new Date("2020-12-20"),
  new Date("2020-11-12"),
];

range.sort((a, b) => a.valueOf() - b.valueOf())