The RegExp Object in JavaScript#

The RegExp object represents a regular expression, which is a text template consisting of ordinary characters and special characters, also known as metacharacters or quantifiers, used for pattern matching in strings.

Description#

There are generally two ways to create a RegExp object: one is by using a literal, and the other is by using the RegExp object constructor.

// var regex = /pattern/modifiers;
var regex = /^[0-9]+$/g;

// var regex = new RegExp("pattern", "modifiers");
var regex = new RegExp("^[0-9]+$", "g");

Where the pattern pattern describes the expression pattern, and the modifiers modifiers are used to specify global matching, case-insensitive matching, multiline matching, and more.

• i: Performs case-insensitive matching.
• g: Performs a global match (finds all matches rather than stopping after the first match).
• m: Performs multiline matching.
• s: Allows the dot . to match newline characters. By default, the dot matches any single character except for a newline character \n, but with the s flag, the dot includes newline characters.
• y: Checks whether the search has sticky properties and only searches at the index indicated by the lastIndex property of the regular expression.
• u: Unicode mode, used to correctly handle Unicode characters larger than \uFFFF, which means it can correctly handle UTF-16 encoding.

RegExp.prototype.compile()#

regexObj.compile(pattern, flags)
The compile() method is used to recompile a regular expression during the script execution process. However, this feature has been removed from the web standard, and the use of the compile() method is not recommended. One can achieve the same effect using the RegExp constructor.

var regex = /^[0-9]+$/g;
regex = regex.compile("^[0-9]+$", "i");
console.log(regex); // /^[0-9]+$/i

RegExp.prototype.exec()#

regexObj.exec(str)
The exec() method executes a search for a match within a specified string and returns an array of results or null. When the global or sticky flags are set, the RegExp object maintains state and records the position of the last successful match in the lastIndex property. Using this feature, exec() can be used to iterate through the results of multiple matches in a single string, including the captured matches. In contrast, String.prototype.match() only returns the matched results.

var regex = /(\d{4})-(\d{2})-(\d{2})/g;
var res = regex.exec("2020-09-02");
console.log(res); // ["2020-09-02", "2020", "09", "02", index: 0, input: "2020-09-02", ... ]

// For complete global regex matching, use RegExp.prototype.exec() or String.prototype.matchAll()
// When using String.prototype.match() with the /g flag to obtain matches, the capture groups will be ignored.
const regMatch = (regex, str) => {
    var result = [];
    var temp = null;
    var flags = `${regex.flags}${regex.flags.includes("g") ? "" : "g"}`; // Must add the g modifier, otherwise it will fall into an endless loop
    regex = new RegExp(regex, flags);
    while (temp = regex.exec(str)) result.push(temp);
    return result;
}

RegExp.prototype.test()#

regexObj.test(str)
The test() method executes a search to determine whether the regular expression matches the specified string and returns true or false.

var regex = /^[0-9]+$/g;
console.log(regex.test("1")); // true

String.prototype.search()#

str.search(regexp)
The search() method executes a search between a regular expression and a String object. If a non-regular expression object regexp is passed, it will be implicitly converted to a regular expression object using new RegExp(regexp). If a match is found, search() returns the index of the first match within the string, otherwise it returns -1.

var regex = /[0-9]+/g;
console.log("s123".search(regex)); // 1

String.prototype.match()#

str.match(regexp)
The match() method retrieves the result of matching a string against a regular expression. If a non-regular expression object is passed, it will implicitly use new RegExp(obj) to convert it to a RegExp. If no parameters are provided and match() is used directly, it will return an array containing an empty string, i.e., [""]. If the g flag is used, it returns all matches of the entire regular expression without the captured groups. If the g flag is not used, it returns only the first complete match and its related capture groups as an Array.

var regex = /(\d{4})-(\d{2})-(\d{2})/g;
var res = "2020-09-02".match(regex);
console.log(res); // ["2020-09-02"]

String.prototype.matchAll()#

str.matchAll(regexp)
The matchAll() method returns an iterator containing all the matches of a regular expression and the captured groups. If a non-regular expression object is passed, it will be implicitly converted to a RegExp using new RegExp(obj). The passed RegExp must be in global mode g, otherwise it will throw a TypeError. It returns an iterator that cannot be reused, and a new iterator must be obtained by calling the method again after the results are exhausted. matchAll internally makes a copy of the regexp, so unlike regexp.exec(), the lastIndex does not change during string scanning.

var regex = /(\d{4})-(\d{2})-(\d{2})/g;
var res = "2020-09-02".matchAll(regex);
console.log([...res]); // You can use the spread operator to expand, or call the next() method for iteration
// [["2020-09-02", "2020", "09", "02", index: 0, input: "2020-09-02", ... ]]

### String.prototype.replace()
`str.replace(regexp|substr, newSubStr|function)`  
The `replace()` method returns a new string with some or all matches of a pattern replaced by a replacement. The pattern can be a string or a regular expression, and the replacement can be a string or a callback function to be invoked for each match. If the pattern is a string, only the first occurrence will be replaced, and the original string will not be changed.

```javascript
var regex = /\d+/g;
var res = "s1s11s111".replace(regex, "");
console.log(res); // sss

String.prototype.split()#

str.split([separator[, limit]])
The split() method splits a String object into an array of strings by separating the string into substrings. The separator specifies where to divide the string, and it can be a string or a regular expression. The limit provides an integer that limits the number of split items returned, and it returns an array of substrings formed by splitting the original string at the occurrence of the separator.

var regex = /\d+/g; // Split by digits
var res = "2020-09-02".split(regex);
console.log(res); // ["", "-", "-", ""]

Properties#

• get RegExp[@@species]: Static property, RegExp[@@species] returns the constructor of RegExp.
• RegExp.lastIndex: lastIndex is a readable and writable integer property of a regular expression, used to specify the starting index for the next match.
• RegExp.prototype.flags: The flags property returns a string consisting of the flags of the current regular expression object.
• RegExp.prototype.dotAll: The dotAll property indicates whether the s modifier is used together in the regular expression.
• RegExp.prototype.global: The global property indicates whether the g modifier is used in the regular expression.
• RegExp.prototype.ignoreCase: The ignoreCase property indicates whether the i modifier is used in the regular expression.
• RegExp.prototype.multiline: The multiline property indicates whether the m modifier is used in the regular expression.
• RegExp.prototype.source: The source property returns the pattern text of the current regular expression object as a string.
• RegExp.prototype.sticky: The sticky property indicates whether the y modifier is used in the regular expression.
• RegExp.prototype.unicode: The unicode property indicates whether the u modifier is used in the regular expression.

Methods#

RegExp.prototype.compile()#

regexObj.compile(pattern, flags)
The compile() method is used to recompile a regular expression during script execution, but this feature has been removed from the Web standard. It is not recommended to use the compile() method, and you can achieve the same effect using the RegExp constructor.

var regex = /^[0-9]+$/g;
regex = regex.compile("^[0-9]+$", "i");
console.log(regex); // /^[0-9]+$/i

RegExp.prototype.exec()#

regexObj.exec(str)
The exec() method executes a search for a match within a specified string and returns the result array, or null. When the global or sticky flags are set, the RegExp object is stateful and it records the index of the last successful match in the lastIndex property. This feature allows exec() to be used for iterating through multiple matches in a single string, including the captured matches, whereas String.prototype.match() will only return the matching results.

var regex = /(\d{4})-(\d{2})-(\d{2})/g;
var res = regex.exec("2020-09-02");
console.log(res); // ["2020-09-02", "2020", "09", "02", index: 0, input: "2020-09-02", ... ]

// To perform a complete global regex match, you can use RegExp.prototype.exec() or String.prototype.matchAll()
// When using String.prototype.match() with the /g flag to obtain matches, the capturing groups will be ignored.
const regMatch = (regex, str) => {
    var result = [];
    var temp = null;
    var flags = `${regex.flags}${regex.flags.includes("g") ? "" : "g"}`; // Must add the g flag, otherwise it will go into an infinite loop
    regex = new RegExp(regex, flags);
    while (temp = regex.exec(str)) result.push(temp);
    return result;
}

RegExp.prototype.test()#

regexObj.test(str)
The test() method performs a search for a match between a regular expression and a specified string, returning true or false.

var regex = /^[0-9]+$/g;
console.log(regex.test("1")); // true

RegExp.prototype[@@match]()#

regexp[Symbol.match](str) When matching a string with a regular expression, the [@@match]() method is used to obtain the matching results. The usage of this method is the same as String.prototype.match(), except for the this and parameter order.

var regex = /(\d{4})-(\d{2})-(\d{2})/g;
var res = regex[Symbol.match]("2020-09-02");
console.log(res); // ["2020-09-02"]

RegExp.prototype[@@matchAll]()#

regexp[Symbol.matchAll](str) The [@@matchAll] method returns all the matching items when a string is used with a regular expression. The usage of this method is the same as String.prototype.matchAll(), except for the this and parameter order.

var regex = /(\d{4})-(\d{2})-(\d{2})/g;
var res = regex[Symbol.matchAll]("2020-09-02");
console.log([...res]); // // [["2020-09-02", "2020", "09", "02", index: 0, input: "2020-09-02", ... ]]

RegExp.prototype[@@replace]()#

regexp[Symbol.replace](str, newSubStr|function) The [@@replace]() method replaces all matching items that conform to the regular pattern in a string with the given replacement, and returns the resulting new string after replacement. The parameter used for replacement can be a string or a callback function for each match. This method can be used similar to String.prototype.replace(), except for the this and parameter order.

var regex = /\d+/g;
var res = regex[Symbol.replace]("s1s11s111", "");
console.log(res); // sss

RegExp.prototype[@@search]()#

regexp[Symbol.search](str) The [@@search]() method executes a search within a given string to find a match with the regular pattern. The usage of this method is the same as String.prototype.search(), except for the this and parameter order.

var regex = /\d+/g;
var res = regex[Symbol.search]("s1s11s111");
console.log(res); // 1

RegExp.prototype[@@split]()#

[@@split]() method splits the String object into an array of substrings. The usage is the same as String.prototype.split(), except for the this and parameter order.

var regex = /\d+/g;
var res = regex[Symbol.split]("2020-09-02");
console.log(res); // ["", "-", "-", ""]

RegExp.prototype.toString()#

regexObj.toString() The toString() method returns a string representing the regular expression.

var regex = /\d+/g;
console.log(regex.toString()); // /\d+/g

Regular Expression Rules#

A list of metacharacter rules and their behaviors in the context of regular expressions. This section is taken from https://www.runoob.com/regexp/regexp-metachar.html.

• \: Marks the next character as either a special character, a literal character, a back reference, or an octal escape character. For example, n matches the character n, \n matches a newline character, the sequence \\ matches \, and \( matches (.
• ^: Matches the start of the input string. If the Multiline property of the RegExp object is set, ^ also matches after a \n or \r.
• $: Matches the end of the input string. If the Multiline property of the RegExp object is set, $ also matches before a \n or \r.
• *: Matches the previous sub-expression zero or more times. For example, zo* can match z or zoo, and * is equivalent to {0,}.
• +: Matches the previous sub-expression one or more times. For example, zo+ can match zo or zoo, but not z, and + is equivalent to {1,}.
• ?: Matches the previous sub-expression zero or one time. For example, do(es)? can match do or does, and ? is equivalent to {0,1}.
• {n}: n is a non-negative integer that matches exactly n times. For example, o{2} does not match the o in Bob, but matches the two os in food.
• {n,}: n is a non-negative integer that matches at least n times. For example, o{2,} does not match the o in Bob, but matches all the os in foooood, where o{1,} is equivalent to o+ and o{0,} is equivalent to o*.
• {n,m}: Both m and n are non-negative integers where n <= m, and it matches at least n times and at most m times. For example, o{1,3} will match the first three os in fooooood, o{0,1} is equivalent to o?, and note that there should be no spaces between the comma and the numbers.
• ?: When this character is placed immediately after any other quantifier (*, +, ?, {n}, {n,}, {n,m}), it makes the matching pattern non-greedy. In non-greedy mode, the pattern matches as little of the searched string as possible, while in the default greedy mode, it matches as much as possible. For example, for the string oooo, o+? will match a single o, while o+ will match all the os.
• .: Matches any single character except for a newline character (\n, \r). To match any character including \n, use a pattern like (.|\n).
• (pattern): Matches pattern and captures the match. The captured match can be obtained from the Matches collection, used with the SubMatches collection in VBScript, or with the $1…$9 properties in JS. To match parentheses characters, use \( or \) .
• (?:pattern): Matches pattern but does not capture the match, which means it is a non-capturing match and is not stored for later use. This is useful when combining different parts of a pattern using the | character. For example, industr(?:y|ies) is a more concise expression than industry|industries.
• (?=pattern): Positive lookahead assertion. Matches at a position where the string following the current position matches pattern. This is a non-capturing match, meaning the match does not need to be stored for later use. For example, Windows(?=95|98|NT|2000) can match Windows in Windows2000, but not in Windows3.1. The lookahead does not consume any characters, it means it immediately starts looking for the next match after the last match instead of starting after the lookahead characters.
• (?!pattern): Negative lookahead assertion. Matches at a position where the string following the current position does not match pattern. This is a non-capturing match, meaning the match does not need to be stored for later use. For example, Windows(?!95|98|NT|2000) can match Windows in Windows3.1, but not in Windows2000. The lookahead does not consume any characters, it means it immediately starts looking for the next match after the last match instead of starting after the lookahead characters.
• (?<=pattern): Positive lookbehind assertion. Works similar to positive lookahead, but in the opposite direction. For example, (?<=95|98|NT|2000)Windows can match Windows in 2000Windows, but not in 3.1Windows.
• (?<!pattern): Negative lookbehind assertion. Works similar to negative lookahead, but in the opposite direction. For example, (?<!95|98|NT|2000)Windows can match Windows in 3.1Windows, but not in 2000Windows.
• x|y: Matches either x or y. For example, z|food can match z or food, and (z|f)ood can match zood or food.
• [xyz]: Character set, matches any one of the characters included. For example, [abc] can match a in plain.
• [^xyz]: Negated character set, matches any character that is not included. For example, [^abc] can match p, l, i, or n in plain.
• [a-z]: Character range, matches any character within the specified range. For example, [a-z] can match any lowercase letter from a to z.
• [^a-z]: Negated character range, matches any character that is not within the specified range. For example, [^a-z] can match any character that is not a lowercase letter from a to z.
• \b: Matches a word boundary, which is the position between a word and a space. For example, er\b can match er in never, but not in verb.
• \B: Matches a non-word boundary. er\B can match er in verb, but not in never.
• \cx: Matches the control character specified by x. For example, \cM matches a Control-M or carriage return. The value of x must be one of A-Z or a-z, otherwise c will be treated as a literal c character.
• \d: Matches a digit character, which is equivalent to [0-9].
• \D: Matches a non-digit character, which is equivalent to [^0-9].
• \f: Matches a form feed character, which is equivalent to \x0c and \cL.
• \n: Matches a newline character, which is equivalent to \x0a and \cJ.
• \r: Matches a carriage return character, which is equivalent to \x0d and \cM.
• \s: Matches any whitespace character, including space, tab, form feed, etc., which is equivalent to [ \f\n\r\t\v].
• \S: Matches any non-whitespace character, which is equivalent to [^ \f\n\r\t\v].
• \t: Matches a tab character, which is equivalent to \x09 and \cI.
• \v: Matches a vertical tab character, which is equivalent to \x0b and \cK.
• \w: Matches a word character, which includes letters, digits, and underscore, and is equivalent to [A-Za-z0-9_].
• \W: Matches a non-word character, which is equivalent to [^A-Za-z0-9_].
• \xn: Matches n, where n is a hexadecimal escape value of two digits. For example, \x41 matches A, and \x041 is equivalent to \x04 followed by 1. This can be used in regular expressions with ASCII encoding.
• \num: Matches num, which is a positive integer and represents a reference to the matched content. For example, (.)\1 matches two consecutive identical characters.
• \n: Indicates an octal escape value or a back reference. If there are at least n captured subexpressions before, then n is a back reference. Otherwise, if n is an octal digit 0-7, then n is an octal escape value.
• \nm: Indicates an octal escape value or a back reference. If there are at least nm captured groupings before, then nm is a back reference. If there are at least n captured groupings before, then n is a back reference followed with the character m. If none of the above conditions are met, and both n and m are octal digits (0-7), then \nm matches the octal escape value nm.
• \nml: If n is an octal digit 0-7 and m and l are also octal digits 0-7, then it matches the octal escape value nml.
• \un: Matches n, where n is a Unicode character represented by four hexadecimal digits. For example, \u00A9 matches the copyright symbol.

Example#

This section comes from https://c.runoob.com/front-end/854.

Validation expression for numbers#

• Number: ^[0-9]+$.
• n-digit number: ^\d{n}$.
• At least n-digit number: ^\d{n,}$.
• m-n digit number: ^\d{m,n}$.
• Number starting with zero or non-zero: ^(0|[1-9][0-9]*)$.
• Non-zero starting number with up to two decimal places: ^([1-9][0-9]*)+(\.[0-9]{1,2})?$.
• Positive or negative number with 1-2 decimal places: ^(\-)?\d+(\.\d{1,2})$.
• Positive, negative, and decimal numbers: ^(\-|\+)?\d+(\.\d+)?$.
• Positive real number with two decimal places: ^[0-9]+(\.[0-9]{2})?$.
• Positive real number with 1-3 decimal places: ^[0-9]+(\.[0-9]{1,3})?$.
• Non-zero positive integer: ^[1-9]\d*$ or ^([1-9][0-9]*){1,3}$ or ^\+?[1-9][0-9]*$.
• Non-zero negative integer: ^\-[1-9][]0-9"*$ or ^-[1-9]\d*$.
• Non-negative integer: ^\d+$or^[1-9]\d*|0$.
• Non-positive integer: ^-[1-9]\d*|0$ or ^((-\d+)|(0+))$.
• Non-negative floating point number: ^\d+(\.\d+)?$or^[1-9]\d*\.\d*|0\.\d*[1-9]\d*|0?\.0+|0$.
• Non-positive floating point number: ^((-\d+(\.\d+)?)|(0+(\.0+)?))$or^(-([1-9]\d*\.\d*|0\.\d*[1-9]\d*))|0?\.0+|0$.
• Positive floating point number: ^[1-9]\d*\.\d*|0\.\d*[1-9]\d*$or^(([0-9]+\.[0-9]*[1-9][0-9]*)|([0-9]*[1-9][0-9]*\.[0-9]+)|([0-9]*[1-9][0-9]*))$.
• Negative floating point number: ^-([1-9]\d*\.\d*|0\.\d*[1-9]\d*)$or^(-(([0-9]+\.[0-9]*[1-9][0-9]*)|([0-9]*[1-9][0-9]*\.[0-9]+)|([0-9]*[1-9][0-9]*)))$.
• Floating point number: ^(-?\d+)(\.\d+)?$ or ^-?([1-9]\d*\.\d*|0\.\d*[1-9]\d*|0?\.0+|0)$.

Validation expression for characters#

• Chinese characters: ^[\u4e00-\u9fa5]{0,}$.
• English and numbers: ^[A-Za-z0-9]+$ or ^[A-Za-z0-9]{4,40}$.
• All characters with a length of 3-20: ^.{3,20}$.
• Strings consisting of 26 English letters: ^[A-Za-z]+$.
• Strings consisting of 26 uppercase English letters: ^[A-Z]+$.
• Strings consisting of 26 lowercase English letters: ^[a-z]+$.
• Strings consisting of numbers and 26 English letters: ^[A-Za-z0-9]+$.
• Strings consisting of numbers, 26 English letters, or underscores: ^\w+$ or ^\w{3,20}$.
• Chinese, English, numbers including underscores: ^[\u4E00-\u9FA5A-Za-z0-9_]+$.
• Chinese, English, numbers but not including underscores and other symbols: ^[\u4E00-\u9FA5A-Za-z0-9]+$ or ^[\u4E00-\u9FA5A-Za-z0-9]{2,20}$.
• Allow input containing ^%&',;=?$\ and other characters: [^%&',;=?$\x22]+.
• Disallow input containing ~ : [^~\x22]+.

Special Requirement Expressions#

• Email Address: ^\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$.
• Domain Name: [a-zA-Z0-9][-a-zA-Z0-9]{0,62}(\.[a-zA-Z0-9][-a-zA-Z0-9]{0,62})+\.?.
• InternetURL: [a-zA-z]+://[^\s]* or ^http://([\w-]+\.)+[\w-]+(/[\w-./?%&=]*)?$.
• Mobile Number: ^(13[0-9]|14[5|7]|15[0|1|2|3|4|5|6|7|8|9]|18[0|1|2|3|5|6|7|8|9])\d{8}$.
• Phone Number XXX-XXXXXXX, XXXX-XXXXXXXX, XXX-XXXXXXX, XXX-XXXXXXXX, XXXXXXX, and XXXXXXXX: ^(\(\d{3,4}-)|\d{3.4}-)?\d{7,8}$.
• Domestic Phone Number (0511-4405222, 021-87888822): \d{3}-\d{8}|\d{4}-\d{7}.
• Phone Number Regular Expression (supporting mobile number, 3-4 digit area code, 7-8 digit local number, 1-4 digit extension): ((\d{11})|^((\d{7,8})|(\d{4}|\d{3})-(\d{7,8})|(\d{4}|\d{3})-(\d{7,8})-(\d{4}|\d{3}|\d{2}|\d{1})|(\d{7,8})-(\d{4}|\d{3}|\d{2}|\d{1}))$).
• ID Number (15 digits, 18 digits, the last one is a check digit, which may be a number or character X): (^\d{15}$)|(^\d{18}$)|(^\d{17}(\d|X|x)$).
• Whether the account is legal (starting with a letter, allowing 5-16 bytes, allowing alphanumeric underscores): ^[a-zA-Z][a-zA-Z0-9_]{4,15}$.
• Password (starting with a letter, between 6~18 characters, can only contain letters, numbers, and underscores): ^[a-zA-Z]\w{5,17}$.
• Strong password (must contain a combination of uppercase and lowercase letters and numbers, cannot use special characters, between 8-10 characters): ^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])[a-zA-Z0-9]{8,10}$.
• Strong password (must contain a combination of uppercase and lowercase letters and numbers, can use special characters, between 8-10 characters): ^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).{8,10}$.
• Date format: ^\d{4}-\d{1,2}-\d{1,2}.
• 12 months of the year (01-09 and 1-12): ^(0?[1-9]|1[0-2])$.
• 31 days in a month (01-09 and 1-31): ^((0?[1-9])|((1|2)[0-9])|30|31)$.
• Money input format, accurate to two decimal places: ^[0-9]+(.[0-9]{1,2})?$.
• xml file: ^([a-zA-Z]+-?)+[a-zA-Z0-9]+\\.[x|X][m|M][l|L]$.
• Regular expression for Chinese characters: [\u4e00-\u9fa5].
• Double-byte characters: [^\x00-\xff] (including Chinese characters, can be used to calculate the length of a string (a double-byte character count as 2, an ASCII character count as 1)).
• Regular expression for blank lines: \n\s*\r (can be used to delete blank lines).
• Regular expression for HTML tags: <(\S*?)[^>]*>.*?|<.*? />.
• Regular expression for leading and trailing whitespace characters: ^\s*|\s*$ or (^\s*)|(\s*$) (can be used to delete leading and trailing whitespace characters (including spaces, tabs, page breaks, etc.)).
• Tencent QQ number: [1-9][0-9]{4,} (Tencent QQ numbers start from 10000).
• Chinese postal code: [1-9]\d{5}(?!\d) (Chinese postal code is 6 digits).
• IP Address: ((?:(?:25[0-5]|2[0-4]\\d|[01]?\\d?\\d)\\.){3}(?:25[0-5]|2[0-4]\\d|[01]?\\d?\\d)).

Daily Topic#

References#