Fourth article, JavaScript

first, Regular Expression

Tip: This topic requires multiple rounds of review and repeated deepening and understanding

Two ways to use regular expressions:

1) regexp.xxx (string);

2) string.yyy (regexp);

Verify that the phone number format entered by the       user is legal var regexp=/^1[3-8]\d{9}$/;         var input="15012345678";        Console.log (regexp.test (input))

Regular expressions are primarily used for form validation

1. Direct Volume characters

Defines a regular expression object that can use Perl-style direct-volume syntax

/pattern/attributes

Description

Direct amount string cannot be added ' or ' (quotation marks) around

Two/not omitted

Parameter pattern is a regular expression string

The parameter attribute is an optional string that can be specified in the range "g", "i" and "m", respectively, to specify global matching, case-sensitive matching, and multi-line matching

2. Character class

All individual uppercase and lowercase letters, numbers are a regular expression that matches a single character, which is the same as itself

        var regexp=/ipod/;         var data='Apple ipod is no.123 cool? ' ;        Console.log (regexp.test (data)); // false        var regexp=/ipod/;         var data='Apple ipod is no.123 cool? ' ;        Console.log (regexp.test (data)); // true

View Code

Regular expressions some characters have special grammatical meanings that cannot be used directly, and must be escaped with \ to be used

. \ / * ? + [ ( ) ] { } ^ $ |

Location matching

^ In/[^123]/matches except for 123

A/^1[123]/that contains 123 and starts with 1.

$ indicates what ends with

| The/[123|456]/represents a match of 123 or 456 of one

A/[123x,]/that matches any of the 123x

\b Indicates the bounds of the matched character

\b The non-boundary example of a matching string: "he is the" so "if it matches his/[/bhis/b in history"

3. Repetition

In regular expressions, you can use the following special characters to define how frequently characters appear---quantifier metacharacters

repeating character   meaning                                  example n?        match 0 or once characters N           /a?/N*         matches 0 or more characters n           /a*/n+        matches once or multiple characters n            /a+/n{x}     match character n occurs x times                 /a{3}/   n{x,y}  match character n appears x to y times              /a{2,4}/    n{x,}    matches the occurrence of the character N >=x times          /a{3,}/

4. selection, Grouping and referencing

Range selection, which specifies a matching range

syntax meaning example [abc] matches any one of the characters in the specified collection/[3458]/[^abc] matches any character that is not in the specified collection/[^12679]/[a-z] matches any lowercase character/[a-z]/[0-9] matches any number/0-9/[A-z] matches any uppercase character/a-z/[A-z] matches all characters of uppercase A through association z,/[a-z]/is a-z[\]^_ ' a-z/[--to]/Exp|EXP2 using | for conditional selection/ex| Ex|post| post/(expl) use () to specify grouping------sub-expression

A regular expression can be simplified by using the following metacharacters reference

 1   syntax meaning example /span>2  \d matches a number/\d/equivalent to/[0
     -9 ]/3  \d matches a non-numeric/\d/, etc. Price At/[^0 -9 ]/ 4  \w matches a number/letter/underscore/\w/equivalent to/[0  -9a-za-z]/ 5  \w matches a non-numeric/character/underscore/\w/equivalent to/[^0  -9a-za-z] /6  \s match a white space character (space)/\s/equivalent To/[\n\r\t\v\f]/7
       \s matches a non-whitespace character/\s/equivalent to/[^\n\r\v\t\f]/8 . Matches any single character except carriage return and line break/./equivalent to/[^\n\r]/

Grouping matches, using () to make a whole number of characters, each of which will automatically get 1, 2, 3 、... Such a grouping

()/(abc) {3}/represents A group of 3 matching groups with ABC

/(abc) (xvv) (xx) 2/mean match (abc) (xvv) these two groupings

/(aa) (bb) (cc)/2/represents A match (bb) for this group

5. Property modifiers in regular expressions

/expression Content/property modifier

The property modifier can be selected within the following three ranges

1) I match ignore case

2) G performs a global match, finds a match and continues, knowing the end

3) M performs a multi-sweat match that affects the meaning of ^ (originally only matches the beginning of the entire String) and $ (which originally only matches the end of the entire string), matching the beginning and end of each line

Fourth article, JavaScript