JavaScript regular expression tips-JS Tutorial-php.cn

This time I will bring you JavaScriptRegular ExpressionsTips,What are thePrecautionsfor using JavaScriptRegular Expressions, the following are practical cases, Let’s take a look.

Regular expressions, as a powerful tool for matching and processing strings, have been widely implemented and used in many languages. This article mainly introduces a summary of JavaScript regular expression functions. Friends in need can refer to it

/* Test environment: Chrome 63.0.3239.132 */

The optional values of regular object modifiers in JS are: "i" "g" "m", which means ignoring case for global matching Multi-line mode

Metacharacters supported by regular expressions in JS:

1: enumerate square bracket expression, range square bracket expression, enumerate inverse square bracket expression, range take Anti-square bracket expression

2: . \w \W \d \D \s \S \b \B \n \r \f \v \888 \uffff \xff

3 ：n? n+ n* n{a} n{a,} n{a,b} and the non-greedy patterns of these quantifiers

4: ^ $ (?!) (?=) (?:)

Others:

1: Please use \number when referencing groups in JS. Named groups such as '' and <> are not supported

2: The possession mode of quantifiers is not supported

3: Reverse lookaround is not supported

4: Compound expressions in square bracket expressions are supported as follows:

[abc0-9] [abc\d] [\d\w^&] and so on

5: Support modifier combinations, such as gim mig gi ig, etc., no order required

JS regular object Properties:

global: whether the object enables global matching, a Boolean value

ignoreCase: whether the object enables ignoring case, a Boolean value

multiline: whether the object Turn on multi-line mode, a Boolean value

lastIndex: the position where the object starts matching next time, that is, the position where the previous matching ends, a positive integer

source: the source text of the regular expression , that is, the regexp of /regexp/flag, does not contain modifiers, a string

Create a regular expression:

1: myreg = new RegExp(patternString[,globalFlags]);

2: myreg = /yourRegexp/globalFlags;

Commonly used regular expression methods in JS:

InRegExp object:

1: test(yourString);

Definition: Test whether a string matches a certain pattern.

Other instructions: This method will ignore the "g" flag and the lastIndex attribute of the regular object (that is, always start from the beginning). As long as a string matching the pattern is found, the match will be successful.

2: exec(yourString);

Definition: Retrieve matches of regular expressions in a string.

Other instructions: If the "g" flag is not turned on, the search is only done once, the lastIndex attribute of the regular object is not modified, and an object is returned, including subscript 0, index, and input. At this time, the attributes are equivalent to match; Turning "g" on will modify the lastIndex property of the regular object to the end position of the substring found this time, and return an object that is the same as if "g" is not turned on. (You can modify the lastIndex attribute of the regular object to specify the position where exec starts to search.)

In the String object:

1: search(yourRegexpOrString);

Definition : Retrieve substrings in a string that match the specified substring or regular expression.

Other instructions: This method will ignore the "g" flag and the lastIndex attribute of the regular object (that is, always start from the beginning), return the position of the first character found, and return -1 if not found.

2: match(yourRegexpOrString);

Definition: Find one or more strings that match a regular expression within a string and return an object. (Ignore the laseIndex attribute)

Other instructions: If the "g" flag is not turned on, only the first matching string will be searched and an object will be returned, including subscript 0, index, input, where subscript 0 Equivalent to index, input is a reference to String; turn on "g" and return an array. The length of the array is the number of matched strings, and each element is the starting character position of each match.

3: replace(yourRegexpOrString,placementString);

Definition: Used to replace some characters with other characters in a string, or replace a substring that matches a regular expression.

Other notes: It will only be replaced once if there is no "g" flag, and always replaced once if the argument is a string rather than a regex object. Returns a string that is the result of replacing yourRegexpOrString with placementString. $ in placementString has special uses, see the following table:

$1, $2, ..., $99	Reference grouping captured in regexp.
$&	The text matched this time.
$`	The text on the left side of the substring matched this time.
$'	The text on the right side of the substring matched this time.
$$	$ itself.

The second parameter of this method can be a function. This function will be called for each match, and the function return value is used as placement. A total of 4 parameters are passed in. One parameter is the subtext matched this time ($&), the middle parameter is the subexpression matching string, the number is not limited ($i), and the second to last parameter is the subscript position of the subtext matched this time. , the last parameter represents the string itself on which the place method is executed.

4: split(yourRegexpOrString[,howMany]);

Definition: Split a string into an array of string values.

Other instructions: It is the reverse operation of arr.join(separatorString). If "" is passed in, each character will be separated into an array. howMany specifies the number of returned arrays.

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!