JavaScript steps to implement a regular expression of date of birth

This article divides the date of birth into several parts and introduces step by step the complete process of implementing a date of birth verification. Friends who are interested in birth date regular expressions can refer to it

Brief introduction

In form validation, regular expressions are often used. Do birth date verification. This article divides the date of birth into several parts and introduces step by step the complete process of implementing a date of birth verification. I believe that after understanding the content of this article, you will have a deeper understanding and stronger confidence in writing regular expressions.

We divide a birth date in the form of 2018-06-15 into three components: year, month and date, and write the corresponding of regularity.

1 Year regular expression

First give the rule definition of year regular expression:

• The year consists of 4 digits

• Only accepts years starting with 19 and 20
  

According to the above rules, it is easy to write the regular expression of the year:

var pattern = /^(19|20)\d{2}$/;
//输出 true
console.log(pattern.test("2008"));

including two / / The slash and the characters in between are the definition of regular expression literals; ^ means matching the beginning of the string, $ means matching the end of the string; ^(19|20) means matching the string starting with 19 or 20, one The function of parentheses is to combine several items into one unit; \d{2} means matching any ASCII number 2 times, \d is equivalent to [0-9], and {2} means matching the previous item 2 times. .

The above regular expression can match the years from 1900 to 2099. If you want to limit the range of years, add the following rules:

• Start of year Ended in 1920

• year ended in 2018
  

According to the above rules, change the regular expression as follows:

var pattern = /^(19[2-9]\d{1})|(20((0[0-9])|(1[0-8])))$/;
//输出 false
console.log(pattern.test("1916"));
//输出 true
console.log(pattern.test("2008"));
//输出 false
console.log(pattern.test("2022"));

##2 month regular

First, give the rule definition of the month regular expression:

• The month can be 1-12

• If the month is 1-9 , then 0

  
  

can be added in front. According to the above rules, the following regular rules and simple tests are given:

##

var pattern = /^((0?[1-9])|(1[0-2]))$/;
//输出 false
console.log(pattern.test("19"));
//输出 true
console.log(pattern.test("02"));
//输出 true
console.log(pattern.test("2"));
//输出 true
console.log(pattern.test("11"));

3 Date regular expressionFirst give the rule definition of date regular expression:

Date It can be 1-31
If the date is 1-9, you can add 0
in front. According to the above rules, the following regular rules and Simple test:

var pattern = /^((0?[1-9])|([1-2][0-9])|30|31)$/;
//输出 false
console.log(pattern.test("32"));
//输出 true
console.log(pattern.test("02"));
//输出 true
console.log(pattern.test("2"));

4 Combination verificationAccording to the above year rules, Month regularity and date regularity combination form the regular expression of date of birth:

var pattern = /^((19[2-9]\d{1})|(20((0[0-9])|(1[0-8]))))\-((0?[1-9])|(1[0-2]))\-((0?[1-9])|([1-2][0-9])|30|31)$/;
//输出 true
console.log(pattern.test("1923-3-18"));
//输出 true
console.log(pattern.test("1923-4-31"));
//输出 true
console.log(pattern.test("1923-2-29"));
//输出 true
console.log(pattern.test("2016-2-29"));

From the above test results, it can be seen that the above regularity verification is not perfect, mainly because Questions about the number of days in 2, 4, 6, 9 and 11 months.

5 ImprovementAccording to the question in step 4, add the limiting rules as follows:

There is no 31st day in April, June, September and November
February has 28 days in ordinary years

• ##February has 29 days in leap years

• Judgment of leap years in ordinary years:

A year that is evenly divisible by 4 is a leap year, and a year that is not evenly divisible by 4 is an ordinary year. But if it is a full hundred years, it is a leap year only if it is divisible by 400, otherwise it is an ordinary year.

Based on the new rules and instructions, the following regular functions and tests are given:

var checkBirth = function (val) {
  var pattern = /^((?:19[2-9]\d{1})|(?:20(?:(?:0[0-9])|(?:1[0-8]))))\-((?:0?[1-9])|(?:1[0-2]))\-((?:0?[1-9])|(?:[1-2][0-9])|30|31)$/;
  var result = val.match(pattern);
  if(result != null) {
    var iYear = parseInt(result[1]);
    var month = result[2];
    var date = result[3];
    if(/^((0?[469])|11)$/.test(month) &&　date == '31') {
      return false;
    } else if(parseInt(month) == 2){
      if((iYear % 4 ==0 && iYear % 100 != 0) || (iYear % 400 == 0)) {
        if(date == '29') {
          return true;
        }
      }
      if(parseInt(date) > 28) {
        return false;
      }
    }
    return true;
  }
  return false;
}
//输出 true
console.log(checkBirth("1923-3-18"));
//输出 false 4月份没有31日
console.log(checkBirth("1923-4-31"));
//输出 false 平年
console.log(checkBirth("1923-2-29"));
//输出 true 闰年
console.log(checkBirth("2016-2-29"));

The above regular expression uses String's match () method, the only parameter of this method is a regular expression, and returns an array composed of matching results. The first element of the array is the matched string, and the remaining elements are subexpressions enclosed in parentheses in the regular expression. The form (:?...) appears many times. This method means that the items are only grouped into one unit, but the characters matching the group are not memorized. This method is used to extract the year, month and day items in the order of regular matching for subsequent comparison.

Based on the above analysis and testing, we not only realized the regular general determination of year, month and day, but also realized the processing of date range and special month days such as 2, 4, 6, 9, and November. , the test results reached the goals we set.

Based on the above explanation and analysis, we can adjust the corresponding limiting rules to meet the project needs in specific scenarios.

Extension

According to the opinion of V2EX netizen xiangyuecn, the above logic code of checkBirth is too much, which is indeed a bit low. Now update the above code as follows:

var checkBirth = function (val) {
  var pattern = /^((19[2-9]\d{1})|(20((0[0-9])|(1[0-8]))))\-((0?[1-9])|(1[0-2]))\-((0?[1-9])|([1-2][0-9])|30|31)$/;
  if(pattern.test(val)) {
    var date = new Date(val);
    var month = val.substring(val.indexOf("-")+1,val.lastIndexOf("-"));
    return date && (date.getMonth()+1 == parseInt(month));
  }
  return false;
}

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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