JavaScript Regular Expressions

RegExp Object

The RegExp object represents a regular expression, which is a powerful tool for performing pattern matching on strings.

Direct volume syntax

/pattern/attributes

Syntax for creating REGEXP objects:

New RegExp (patternattributes);

Parameters

pattern is a string that specifies the pattern of a regular expression or other regular expression. In a string, RegExp is a special character. We must escape ("/") if we want to use it!

The parameter attributes is an optional string that contains the property "G", "I", and "M", respectively, for specifying global matching, case-sensitive matching, and multiline matching. The M attribute is not supported until ECMAScript is normalized. If pattern is a regular expression, not a string, you must omit the parameter.

* Regular expressions are composed of two basic characters:

1. literal literal characters
2. Metacharacters

* Metacharacters are non-alphabetic characters that are unique in regular expressions

These symbols are: ^ $. * +  - ? = ! : | \ / ( ) [ ] { }

1. "[]" denotes a character class: that is, in parentheses is a character set, indicating the scope of: such as/[abc]/, the expression and contains any one letter of the string are matched, in the [] composition of the class can be ligatures, such as: [A-za-z].

Note: Special character classes: \s represents space characters, tab characters, Unicode whitespace characters. \s represents a non-Unicode whitespace character. (You can also customize the Unicode character class:

/[\u4e00-\u9fa5]/indicates that only Chinese characters are matched. )

\w any single character, equivalent to [a-za-x0-9_];\w and \w.

\d any number, equivalent to [0-9];\d and \w opposite.

\b is used in character classes to represent BACKSPACE. [\b] Indicates the direct amount of the backspace. \b can be used to specify a matching position, or it can be called an anchor, such as:

Find the word Java in a sentence, you can use/\bjava\b/;\b instead.

2. "-" means hyphens, such as [A-z];

3. "." Represents any character except newline characters and other Unicode line terminators.

4. "^" has a twofold meaning: start tag and non, such as:/^a/represents a character starting with a, when in []:/[^a]/represents all characters other than a.

5. "$" indicates the end of the character. For example:/^abc$/represents a character ending with C.

6. "{}" means repeating the previous item. If/\d{2,4}/indicates that the number appears two times, it appears up to 4 times. such as/3{2,4}/match 33 ... ; 333 ..... ; 3333...; Mismatch between 3 and 4 3 is connected above. Its three formats are as follows {N,m} representing at least 3 times, up to M times, {n,} at least n times, and {n} exactly n times.

7. "?" Represents {0,1}.

8. "+" means {1,}.

9. "*" means {0,}.

Note: non-greedy duplicates (such as??, +?,*?,{1,5}? Match only the first one, as long as you add a question mark after the quantifier. ）

10. "|" Represents the meaning of segmentation, even if. such as:/ab|cd|ef/matches a string containing AB or CD or EF.

11. "()" contains a threefold purpose: one is to define sub-expressions. The second is to define the sub-pattern in the complete pattern. The third is a reference to the subexpression.

The definition of a sub-pattern can be extracted from the target string and matched to the sub-pattern in parentheses.

A reference to the expression of a sub-pattern refers to a number that recognizes the sub-pattern and extracts it. such as/(ABC) \sis\s (string\w*)/; contains two words expression: can be

\1 means (ABC); \2 (string\w*); application as:/[' "] [^' "] *[' "] /cannot take the same quotation marks, can write:/[(' ") [^' "] *\1]/, can play a binding role.

Note: If you want to not be remembered, you can use (?: ...), it will not be numbered.

and (? =p), (?! p) as follows:

such as/(JavaScript)? (? =\:)/Indicates matching javascript:, but does not contain:; it does not match JavaScript, because he has a condition to be followed:;

(?! P) Anti-forward declaration, which requires that the next character does not match the pattern p, as opposed to (? =p).

12. Grouping:

Reverse reference:

Prospect:

Methods of regular Expressions:

RegExp.prototype.test ()

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JavaScript Regular Expressions