Issues with code execution in JavaScript caused by faulty Regex expressions

Question

Issues with code execution in JavaScript caused by faulty Regex expressions

Looking for a solution to create a capture and test program for a unique date format that isn't compatible with Date.parse (results in NaN) using the following RegEx:

/(\d{1,2})\/(\d{1,2})\/(\d{2,4})/ //day/month/year

While it works on the rubular tester, using it in Chrome produces unexpected results:

dateRegex.test("19111/7/1992")
> true
"19111/7/1992".match(dateRegex) //Intentionally incorrect
> ["11/7/1992", "11", "7", "1992"] //Why is it matching 11?

Are there any JavaScript RegEx nuances that I should take into consideration?

javascript regex

Answer 1

Answer №1

Other answers have thoroughly explained the actual matching routine.

If you want to further verify the date, you can use a function like this:

function verifyDate(d) {
    var v, m = d.match(/^(\d{1,2})\/(\d{1,2})\/(\d{1,4})$/);
    if (!m)
        return false;
    v = new Date(m[3], m[2] - 1, m[1]);
    return m[1] == v.getDate() &&
        m[2] == v.getMonth() + 1 &&
        m[3] == v.getFullYear()
    ;
}

Alternatively, you can use a potentially faster function:

function verifyDate(d) {
    function leap(y) {
        return !((y%4)||(!(y%100) && (y%400)));   
    }
    var m = d.match(/^(\d{1,2})\/(\d{1,2})\/(\d{1,4})$/);

    //  No match || date or month is below 1, or month is above 12
    if (!m || m[1] < 1 || m[2] < 1 || m[2] > 12) {
        return false;
    // Jan,Mar,May,Jul,Aug,Oct,Dec
    } else if ([2,4,6,9,11].indexOf(+m[2]) < 0) {
        return m[1] < 32;
    // Feb
    } else if (m[2] === '2') {
        return m[1] < 29 ? true :
            m[1] < 30 && leap(+m[3]);
    // Apr,Jun,Sep,Nov
    } else {
        return m[1] < 31;
    }
}

Answer 2

Other answers have thoroughly explained the actual matching routine.

If you want to further verify the date, you can use a function like this:

function verifyDate(d) {
    var v, m = d.match(/^(\d{1,2})\/(\d{1,2})\/(\d{1,4})$/);
    if (!m)
        return false;
    v = new Date(m[3], m[2] - 1, m[1]);
    return m[1] == v.getDate() &&
        m[2] == v.getMonth() + 1 &&
        m[3] == v.getFullYear()
    ;
}

Alternatively, you can use a potentially faster function:

function verifyDate(d) {
    function leap(y) {
        return !((y%4)||(!(y%100) && (y%400)));   
    }
    var m = d.match(/^(\d{1,2})\/(\d{1,2})\/(\d{1,4})$/);

    //  No match || date or month is below 1, or month is above 12
    if (!m || m[1] < 1 || m[2] < 1 || m[2] > 12) {
        return false;
    // Jan,Mar,May,Jul,Aug,Oct,Dec
    } else if ([2,4,6,9,11].indexOf(+m[2]) < 0) {
        return m[1] < 32;
    // Feb
    } else if (m[2] === '2') {
        return m[1] < 29 ? true :
            m[1] < 30 && leap(+m[3]);
    // Apr,Jun,Sep,Nov
    } else {
        return m[1] < 31;
    }
}

Answer 3

Answer №2

Consider utilizing

^(\d{1,2})\/(\d{1,2})\/(\d{2,4})$

^ signifies the start of the string, while $ signifies the end of the string (or before a line break at the end, if present).

Answer 4

Consider utilizing

^(\d{1,2})\/(\d{1,2})\/(\d{2,4})$

^ signifies the start of the string, while $ signifies the end of the string (or before a line break at the end, if present).

Answer 5

Answer №3

It is important to note that handling dates requires precision, as incorrect parsing can lead to unexpected results. As you may already know, using a generic method can result in parsing invalid dates such as 99/99/9999.

Regarding the scenario where 11/7/1992 was parsed, this likely occurred due to the absence of boundaries in the parsing logic, allowing partial matches within a string. There are various approaches to rectify this issue.

One solution involves enforcing strict matching by utilizing anchors like ^ and $ to signify the start and end of the string, respectively.

/^(\d{1,2})\/(\d{1,2})\/(\d{2,4})$/

Alternatively, incorporating \b to signify word boundaries can help parse dates located within a larger string.

/\b(\d{1,2})\/(\d{1,2})\/(\d{2,4})\b/

Answer 6

It is important to note that handling dates requires precision, as incorrect parsing can lead to unexpected results. As you may already know, using a generic method can result in parsing invalid dates such as 99/99/9999.

Regarding the scenario where 11/7/1992 was parsed, this likely occurred due to the absence of boundaries in the parsing logic, allowing partial matches within a string. There are various approaches to rectify this issue.

One solution involves enforcing strict matching by utilizing anchors like ^ and $ to signify the start and end of the string, respectively.

/^(\d{1,2})\/(\d{1,2})\/(\d{2,4})$/

Alternatively, incorporating \b to signify word boundaries can help parse dates located within a larger string.

/\b(\d{1,2})\/(\d{1,2})\/(\d{2,4})\b/

Answer 7

Answer №4

It appears that your regex is functioning correctly. Here's a breakdown of what's happening:

19111/7/1992
   ^
   Match begins at this point, with any characters before being ignored

To ensure that your regex only matches the entire string from start to finish, you'll need to include anchors at the beginning and end:

/^(\d{1,2})\/(\d{1,2})\/(\d{2,4})$/

Make sure to take note of the ^ and $ symbols, as they prevent any additional characters at the start or end of the string from passing the regex test.

Answer 8

It appears that your regex is functioning correctly. Here's a breakdown of what's happening:

19111/7/1992
   ^
   Match begins at this point, with any characters before being ignored

To ensure that your regex only matches the entire string from start to finish, you'll need to include anchors at the beginning and end:

/^(\d{1,2})\/(\d{1,2})\/(\d{2,4})$/

Make sure to take note of the ^ and $ symbols, as they prevent any additional characters at the start or end of the string from passing the regex test.

Issues with code execution in JavaScript caused by faulty Regex expressions

Answer №1

Answer №2

Answer №3

Answer №4

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