JavaScript's regular expression does not fully match until the end of the given string

Question

JavaScript's regular expression does not fully match until the end of the given string

In my JavaScript code, I am validating dates using a regular expression. The specific regular expression I am utilizing is as follows:

/^(((((0?[1-9])|(1\d)|(2[0-8]))\/((0?[1-9])|(1[0-2])))|((31\/((0?[13578])|(1[02])))|((29|30)\/((0?[1,3-9])|(1[0-2])))))\/((20[0-9][0-9])|(19[0-9][0-9])))|((29\/02\/(19|20)(([02468][048])|([13579][26]))))$/

While this regular expression accurately matches valid dates, there is an issue where it would also match values with additional characters following the date, disregarding the $ end of string marker. For example, it would match "1/1/2001ff" even though $ is used to denote the end of the string. However, if the additional characters are placed before the date, like "ff1/1/2001", it would correctly invalidate the date. This suggests that the regular expression is prioritizing the start of the string and ignoring the end part.

If anyone has insights into why this behavior occurs, please share.

javascript regex

Answer 1

Answer №1

Source: Identifying an "invalid date" Date object in JavaScript

if ( Object.prototype.toString.call(date) === "[object Date]" ) {
  // it is a date
  if ( isNaN( date.getTime() ) ) {  // date.valueOf() could also be used
    // date is not valid
  }
  else {
    // date is valid
  }
}
else {
  // not a date
}

It is more logical to check if a date is valid rather than using regex to match a date. Although, if you need to search for dates, regex can still be effective. However, as mentioned in the comment, a complex regex is not necessary.

Answer 2

Source: Identifying an "invalid date" Date object in JavaScript

if ( Object.prototype.toString.call(date) === "[object Date]" ) {
  // it is a date
  if ( isNaN( date.getTime() ) ) {  // date.valueOf() could also be used
    // date is not valid
  }
  else {
    // date is valid
  }
}
else {
  // not a date
}

It is more logical to check if a date is valid rather than using regex to match a date. Although, if you need to search for dates, regex can still be effective. However, as mentioned in the comment, a complex regex is not necessary.

Answer 3

Answer №2

Highlighted by Dracs, the error stemmed from a lack of brackets. Much appreciation for bringing this to our attention. We opted not to utilize the javascript date object due to our requirement of exclusively permitting mm/dd/yyyy format in the input field. Utilizing a regex for textbox validation proved to be a straightforward solution.

Answer 4

Highlighted by Dracs, the error stemmed from a lack of brackets. Much appreciation for bringing this to our attention. We opted not to utilize the javascript date object due to our requirement of exclusively permitting mm/dd/yyyy format in the input field. Utilizing a regex for textbox validation proved to be a straightforward solution.

JavaScript's regular expression does not fully match until the end of the given string

Answer №1

Answer №2

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