Basics of Regular Expressions in js, regular expressions in js

Basics of Regular Expressions in js, regular expressions in js

Definition: regular expressions are used to specify the content retrieved in the text. It is a powerful tool for matching string execution modes.

RegExp (Regular Expression) object Syntax: new RegExp (pattern, attributes );

Pattern is a string or matching rule.

Attributes is an optional string, including attributes g, I, and m

G: indicates global match (continue matching)

I: Indicates case-insensitive matching.

M: Indicates multi-row matching. It is only useful for the ^ and $ modes.

Regular Expressions can be defined in two forms:

Constructor: new RegExp (pattern, attributes); example: var reg = new RegExp ("abc", "g "); the regular expression in the constructor can be a constant string or a js variable.

Normal Mode:/pattern/attributes (/regular/attribute) Example: var reg =/abc/g; regular mode must be a constant string

Each regular expression has a lastIndex attribute, which is used to record the position (index value) of the last match ).

Obtain reg. lastIndex and set reg. lastIndex = 0;

Example: var str = 'abcdefg ';

Var reg = new RegExp ('AB', 'G ');

Alert (reg. test (str ));

Alert (reg. lastIndex); // 2

Metacharacters:

\ D: match any number, 0 ~ Any one of the 9

\ S: matches any blank character

\ B: match a word boundary. It does not match any characters.

\ W: match any character (letters, numbers, and underscores).: match any character, except for line breaks (\ n)

\ N: Find the line break

\ U: usually used to match Chinese Characters

The expression "\ d", "\ s", "\ B", "\ w". The corresponding uppercase letter indicates the opposite meaning, for example: \ D matches all non-numeric characters.

Square brackets:

[Abc]: searches for any character between square brackets.

[^ Abc]: searches for any character that is not in square brackets.

[0-9]: searches for any number ranging from 0 to 9.

[A-z]: searches for any characters from lowercase to lowercase.

[A-Z]: Find any character from uppercase A to uppercase Z.

Quantifiers:

N +: match any string containing at least one n.

N? : Match any string containing zero or one n.

N *: match any string containing zero or more n characters.

N {X}: string that matches X n sequences.

N {X, Y}: string that matches the sequence of X to Y n.

^ N: match any string starting with n.

N $: match any string ending with n.

Others:

|: Match the Left or Right

\: Special punctuation marks of the escape character. After \ is added, it indicates the character itself.

^ To match the character "^", use \ ^

() To match the parentheses themselves, use \ (and \) Other special Punctuation Marks [] {}.? + * |

Unicode-encoded hexadecimal UTF-8 Chinese character encoding: 4e00 minimum Chinese Character 9fa5 maximum Chinese Character

/^ [\ U4e00-\ u9fa5] + $ // common Chinese character encoding range

RegExp object Method

Test: returns true or false reg. test (str) for the specified value in the search string );

Exec: retrieves the string and returns the first value of the search result, reg.exe c (str );

Compile: This method can re-edit the specified Regular Expression var reg = new RegExp ("13 [4-9] (\ d) {8}", "g ");

// Re-edit the regular expression reg. compile ("13 [0-3] (\ d) {8}", "g ");

String object Method

Search: Use str. search (reg); (Return Index value, no-1)

Match: returns matching of all regular expressions (plus g) usage: str. match (reg); (returns an array)

Replace: replace the substring that matches the regular expression. Usage: str. replace (reg ,"");

Split: splits (removes) matching strings. Usage: str. split (reg); (returns an array)

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