How to judge whether the date is reasonable in javascript

With the development of the Internet, more and more websites or applications need to involve date calculation or verification. In JavaScript, determining whether a date is reasonable is a common problem. So, how to judge whether the date is reasonable? Next, let’s discuss it together.

1. Date format

Before judging whether the date is reasonable, you first need to confirm whether the entered date format is correct. There are three common date formats:

1. yyyy/MM/dd
2. yyyy-MM-dd
3. yyyy年MMmonthdd日

Where, yyyy represents the year, MM represents the month, and dd represents day.

Among them, the first two date formats are more common and are also the most common date formats in development.

2. Leap Year Judgment

When judging whether the date is reasonable, you first need to judge whether the year is a leap year.

The definition of leap year: A Gregorian calendar year that is a multiple of 4 and not a multiple of 100 is a leap year; a Gregorian calendar year that is a multiple of 400 is also a leap year. For example: 2000 is a leap year, but 1900 is not a leap year.

In JavaScript, the code for judging leap years is as follows:

function isLeapYear(year) {
  return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
}

3. Date verification

With the basis for leap year judgment, the date can be verified next. . Specifically, for a date string, it can be verified as follows:

1. Use regular expressions to check whether the date format conforms to the specification
2. Separate the year, month, and day Extract it
3. Verify the month, the month should be between 1-12
4. Verify the day, the range of the day should be between 1-31, but according to different months In the case of leap years, the range of days may be different

The following are the specific steps and code implementation:

Regular expression verification format

function checkDate(dateStr) {
  var reg = /^(\d{4})(\/|-|\u5e74)(\d{1,2})(\/|-|\u6708)(\d{1,2})/;
  return reg.test(dateStr);
}

Year, month and day extraction

function getDateInfo(dateStr) {
  var dateArr;
  if (dateStr.indexOf('/') != -1) {
    dateArr = dateStr.split('/');
  } else if (dateStr.indexOf('-') != -1) {
    dateArr = dateStr.split('-');
  } else {
    dateArr = dateStr.split('\u5e74');
    dateArr[1] = dateArr[1].replace('\u6708', '');
    dateArr[2] = dateArr[2].replace('\u65e5', '');
  }
  return {
    year: parseInt(dateArr[0]),
    month: parseInt(dateArr[1]),
    day: parseInt(dateArr[2])
  }
}

Month verification

function checkMonth(month) {
  return month >= 1 && month <= 12;
}

Day verification

function checkDay(year, month, day) {
  var maxDay;
  switch (month) {
    case 1:
    case 3:
    case 5:
    case 7:
    case 8:
    case 10:
    case 12:
      maxDay = 31;
      break;
    case 4:
    case 6:
    case 9:
    case 11:
      maxDay = 30;
      break;
    case 2:
      if (isLeapYear(year)) {
        maxDay = 29;
      } else {
        maxDay = 28;
      }
      break;
    default:
      return false;
  }
  return day >= 1 && day <= maxDay;
}

4. Summary

Through the explanation of date format, leap year and date verification, I believe that everyone can learn how to judge whether the date is reasonable. Of course, it may be difficult to implement, and you need to practice more in practice. I hope this article is helpful to everyone, thank you for reading.

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