Dates Flashcards

Question

If hours/minutes/seconds/ms is absent, what are they assumed to be?

Answer 1

they are assumed to be equal 0.

Answer 2

Date.prototype.getMonth() | Get the month, from 0 to 11.

Answer 3

Date.prototype.getHours() Date.prototype.getMinutes() Date.prototype.getSeconds() Date.prototype.getMilliseconds()

Answer 4

``` Date.prototype.getUTCMonth() Date.prototype.getUTCFullYear() Date.prototype.getUTCDay() Date.prototype.getUTCHours() Date.prototype.getUTCMilliseconds() ```

Answer 5

Date.prototype.getTime()

Answer 6

Date.prototype.getTimezoneOffset()

Answer 7

Date.prototype.setFullYear(year, [month], [date]) Date.prototype.setMonth(month, [date]) Date.prototype.setDate(date) Date.prototype.setHours(hour, [min], [sec], [ms]) Date.prototype.setMinutes(min, [sec], [ms]) Date.prototype.setSeconds(sec, [ms]) Date.prototype.setMilliseconds(ms) Date.prototype.setTime(milliseconds) (sets the whole date by milliseconds since 01.01.1970 UTC)

Answer 8

Date.prototype.setUTCFullYear(year, [month], [date]) Date.prototype.setUTCMonth(month, [date]) Date.prototype.setUTCDate(date) Date.prototype.setUTCHours(hour, [min], [sec], [ms]) Date.prototype.setUTCMinutes(min, [sec], [ms]) Date.prototype.setUTCSeconds(sec, [ms]) Date.prototype.setUTCMilliseconds(ms)

Answer 9

...is 1st Feb 2013! | it autocorrects

Answer 10

``` let date = new Date(); date.setSeconds(date.getSeconds() + 70); ```

Answer 11

``` // min day is 1, so the last day of the previous month is assumed // 31 Dec 2015 ```

Answer 12

Converts to ms since 1970 145633456457 NaN (this was a string)

Answer 13

t | it doesn't have to create an object first

Answer 14

``` function diffSubtract(date1, date2) { return date2 - date1; } ``` ``` function diffGetTime(date1, date2) { return date2.getTime() - date1.getTime(); } ``` ``` function bench(f) { let date1 = new Date(0); let date2 = new Date(); ``` ``` let start = Date.now(); for (let i = 0; i < 100000; i++) f(date1, date2); return Date.now() - start; } ``` ``` let time1 = 0; let time2 = 0; ``` ``` // run bench(diffSubtract) and bench(diffGetTime) each 10 times alternating for (let i = 0; i < 10; i++) { time1 += bench(diffSubtract); time2 += bench(diffGetTime); } ``` alert( 'Total time for diffSubtract: ' + time1 ); alert( 'Total time for diffGetTime: ' + time2 );

Answer 15

// added for "heating up" prior to the main loop bench(diffSubtract); bench(diffGetTime); ``` // now benchmark for (let i = 0; i < 10; i++) { time1 += bench(diffSubtract); time2 += bench(diffGetTime); } ``` Modern JavaScript engines start applying advanced optimizations only to “hot code” that executes many times (no need to optimize rarely executed things). So, in the example above, first executions are not well-optimized. We may want to add a heat-up run: (but better to just learn about what are the best ways to do something. there are many optimizations and contexts we may not know about)

Answer 16

'YYYY-MM-DDTHH:mm:ss.sssZ' let ms = Date.parse('2012-01-26T13:51:50.417-07:00'); (it's not dash 07:00. It's + or - '2012-01-26T13:51:50.417+07:00')

Answer 17

``` let date = new Date( Date.parse('2012-01-26T13:51:50.417-07:00') ); But you don't have to: let date = new Date('2012-01-26T13:51:50.417-07:00'); ```

Answer 18

``` function getDateAgo(date, days) { date.setDate(date.getDate() - days); return date.getDate(); } ```

Answer 19

``` function getLastDayOfMonth(year, month) { let date = new Date(year, month + 1, 0); return date.getDate(); } ``` alert( getLastDayOfMonth(2012, 0) ); // 31 alert( getLastDayOfMonth(2012, 1) ); // 29 alert( getLastDayOfMonth(2013, 1) ); // 28

Answer 20

``` function getSecondsToday() { let now = new Date(); ``` ``` // create an object using the current day/month/year let today = new Date(now.getFullYear(), now.getMonth(), now.getDate()); ``` ``` let diff = now - today; // ms difference return Math.round(diff / 1000); // make seconds } ``` alert( getSecondsToday() ); OR ``` function getSecondsToday() { let d = new Date(); return d.getHours() * 3600 + d.getMinutes() * 60 + d.getSeconds(); } ``` alert( getSecondsToday() ); OR

Answer 21

``` function formatDate(date) { let diff = new Date() - date; // the difference in milliseconds ``` if (diff < 1000) { // less than 1 second return 'right now'; } let sec = Math.floor(diff / 1000); // convert diff to seconds if (sec < 60) { return sec + ' sec. ago'; } ``` let min = Math.floor(diff / 60000); // convert diff to minutes if (min < 60) { return min + ' min. ago'; } ``` ``` // format the date // add leading zeroes to single-digit day/month/hours/minutes let d = date; d = [ '0' + d.getDate(), '0' + (d.getMonth() + 1), '' + d.getFullYear(), '0' + d.getHours(), '0' + d.getMinutes() ].map(component => component.slice(-2)); // take last 2 digits of every component ``` ``` // join the components into date return d.slice(0, 3).join('.') + ' ' + d.slice(3).join(':'); } ``` alert( formatDate(new Date(new Date - 1)) ); // "right now" alert( formatDate(new Date(new Date - 30 * 1000)) ); // "30 sec. ago" alert( formatDate(new Date(new Date - 5 * 60 * 1000)) ); // "5 min. ago" ``` // yesterday's date like 31.12.2016 20:00 alert( formatDate(new Date(new Date - 86400 * 1000)) ); ``` OR ``` function formatDate(date) { let dayOfMonth = date.getDate(); let month = date.getMonth() + 1; let year = date.getFullYear(); let hour = date.getHours(); let minutes = date.getMinutes(); let diffMs = new Date() - date; let diffSec = Math.round(diffMs / 1000); let diffMin = diffSec / 60; let diffHour = diffMin / 60; ``` ``` // formatting year = year.toString().slice(-2); month = month < 10 ? '0' + month : month; dayOfMonth = dayOfMonth < 10 ? '0' + dayOfMonth : dayOfMonth; hour = hour < 10 ? '0' + hour : hour; minutes = minutes < 10 ? '0' + minutes : minutes; ``` ``` if (diffSec < 1) { return 'right now'; } else if (diffMin < 1) { return `${diffSec} sec. ago` } else if (diffHour < 1) { return `${diffMin} min. ago` } else { return `${dayOfMonth}.${month}.${year} ${hour}:${minutes}` } } ```