Created
August 5, 2020 03:52
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javascript code to get next day of the week
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| <html> | |
| <body> | |
| <div id="content"></div> | |
| <script> | |
| const DaysOfTheWeek = | |
| { | |
| SUNDAY: 0, | |
| MONDAY: 1, | |
| TUESDAY: 2, | |
| WEDNESDAY: 3, | |
| THURSDAY: 4, | |
| FRIDAY: 5, | |
| SATURDAY: 6, | |
| } | |
| Object.freeze(DaysOfTheWeek) | |
| function getNextDayOfWeek(sourceDate, targetDayOfWeek, forceToNextWeek = false) | |
| { | |
| var resultDate = new Date(sourceDate) // force a copy so we don't modify the original object | |
| var dayOfWeek = targetDayOfWeek % 7 // fix input if it's too large - ideally we'd throw an exception, but it's not like this is formal code | |
| var dayOffset = (7 /* go to next week */ + dayOfWeek /* go to the day we want */ - sourceDate.getDay() /* minus what we already are */) | |
| if (!forceToNextWeek) | |
| { | |
| dayOffset = dayOffset % 7 | |
| } | |
| var dayOfMonthForNextWeekday = resultDate.getDate() + dayOffset | |
| // this is magic, if your specified date goes into next month, it does the maths for us :) | |
| resultDate.setDate(dayOfMonthForNextWeekday); | |
| return resultDate; | |
| } | |
| // TEST CODE, you don't need this: | |
| function printTestResult(testResult) | |
| { | |
| if (testResult) return "✅" | |
| return "❌" | |
| } | |
| function appendText(html) | |
| { | |
| document.getElementById("content").innerHTML += html | |
| } | |
| var startDate = new Date() // today | |
| var firstMonth = startDate.getMonth() | |
| var testResult = "" | |
| appendText("Today's date:<br />" + startDate + "<br />"); | |
| // These aren't... super rigorous, but whatever. | |
| var firstSunday = getNextDayOfWeek(startDate, DaysOfTheWeek.SUNDAY) | |
| appendText("<br />This better be a sunday: " + printTestResult(firstSunday.getDay() == DaysOfTheWeek.SUNDAY) +"<br />" + firstSunday + "<br />") | |
| var nextSunday = getNextDayOfWeek(firstSunday, DaysOfTheWeek.SUNDAY) | |
| appendText("<br />Make sure this is the same date as above, because we're not forcing the next week: ") | |
| appendText(printTestResult(firstSunday.getTime() == nextSunday.getTime()) + "<br />" + nextSunday + "<br />"); | |
| var forcedNextSunday = getNextDayOfWeek(nextSunday, DaysOfTheWeek.SUNDAY, true) | |
| appendText("<br />Make sure this is the sunday after the week above, because we're forcing the week: ") | |
| appendText(printTestResult(forcedNextSunday > nextSunday)); | |
| appendText("<br />" + nextSunday + "<br />"); | |
| nextWednesday = getNextDayOfWeek(forcedNextSunday, DaysOfTheWeek.WEDNESDAY, true) | |
| appendText("<br />Make sure this is a Wednesday: ") | |
| appendText(printTestResult(nextWednesday.getDay() == DaysOfTheWeek.WEDNESDAY)); | |
| appendText("<br />" + nextWednesday + "<br />") | |
| nextSunday = getNextDayOfWeek(nextWednesday, DaysOfTheWeek.SUNDAY, true) | |
| // guarantee we cross over to the next month: | |
| nextSunday = getNextDayOfWeek(nextSunday, DaysOfTheWeek.SUNDAY, true) | |
| nextSunday = getNextDayOfWeek(nextSunday, DaysOfTheWeek.SUNDAY, true) | |
| appendText("<br />Make sure it crosses over month since first date: " + printTestResult(nextSunday.getMonth != firstMonth) + "<br />" + nextSunday + "<br />"); | |
| // Just sanity checking: | |
| appendText("<br />This should not be a tick: " + printTestResult(false)) | |
| </script> | |
| </body> | |
| </html> |
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