RegExp Object

RegExp Object
A regular expression is an object that describes a pattern of characters.Regular expressions are used to perform pattern-matching and "search-and-replace" functions on text.

Syntax

var patt=new RegExp(pattern,modifiers);
or more simply:
var patt=/pattern/modifiers;

Remarks :
• pattern specifies the pattern of an expression for example "abcd" String pattern to find among string value

• modifiers specify if a search should be global, case-sensitive, or on multilines , modifiers can be mixed up together such as /patt/gim or /patt/gi ... etc , the mixing depends on the developer needs , Modifiers are used to perform case-insensitive and global searches , the main values are :

o i : Perform case-insensitive matching
o g : Perform a global match (find all matches rather than stopping after the first match)
o m : Perform multiline matching
Brackets
Brackets are used to find a range of characters that are specified inside these brakets "[]" , for example to find all numbers inside given string , you can describe the pattern as [the lowest number - the heighest number] as shown in the following examples :

Example 1 :
var myString= my age is 27 because my bd is 1985 / 1/ 4
patt1=/[0-8]/g;
document.write(str.match(patt1));
the output will be : 1,2,4,7,8 // but not 9 because its out the range


Example 2 :
var myString= my age is 27 because my bd is 1985 / 1/ 4
patt1=/[a-d]/gi;
document.write(str.match(patt1));
The output will be : a,b,c,a,b,d // only the characters in the string that are in the range a to d

Example 3:
var myString= my age is 27 because my bd is 1985 / 1/ 4
patt1=/[m,y,s,4]/gi;
document.write(str.match(patt1));
The output will be m,y,s,m,y,4

The Full Forms of a Pattern Modifier can be one of the following only :

• [abc] Find any character between the brackets
• [^abc] Find any character not between the brackets
• [0-9] Find any digit from 0 to 9
• [A-Z] Find any character from uppercase A to uppercase Z
• [a-z] Find any character from lowercase a to lowercase z
• [A-z] Find any character from uppercase A to lowercase z
• [adgk]Find any character in the given set
• [^adgk] Find any character outside the given set

Metacharacters
Metacharacters are characters with a special meaning:

• . Find a single character, except newline or line terminator
• \w Find a word character
• \W Find a non-word character
• \d Find a digit
• \D Find a non-digit character
• \s Find a whitespace character
• \S Find a non-whitespace character
• \b Find a match at the beginning/end of a word
• \B Find a match not at the beginning/end of a word
• \n Find a new line character
• \r Find a carriage return character
• \t Find a tab character
• \v Find a vertical tab character

Notes :
1. The \s metacharacter is used to find a whitespace character. A whitespace character can be:

• A space character
• A tab character
• A carriage return character
• A new line character
• A vertical tab character

2. The \n character is used to find a newline character. The \n returns the position where the newline character was found. If no match is found, it returns -1.






Examples :

#1 : Do a global search for digits:
var str="Give 100%!"; var patt1=/\d/g;
The marked text shows where the expression gets a match: Give 100%!



#2 : Do a global search for whitespace characters in a string:
var str="Is this all there is?"; var patt1=/\s/g;
All the spaces in the text will get a match (four matches): Is this all there is?



#3 : Do a global search for "www" at the beginning or end of a word in a string:
var str="Visit www.uobabylon.edu.iq"; var patt1=/\bwww/g;
The marked text shows where the expression gets a match: www.uobabylon.edu.iq



#4 : Search for a newline character in a string:
var str="check Links \n www.uobabylon.edu.iq \n repository.uobabylon.com"; var patt1=/\n/;
The marked text shows where the expression gets a match:11

The \n Modifier only finds the first one when used with search() , and finds non when used with match() , but it works very well with Array String retruned string object methods like substring() or replace() , Example :

var str="check Links\n www.uobabylon.edu.iq\n repository.uobabylon.com";
var patt1=/\n/g;
document.write(str.replace(patt1,
));




#5: Search for a single character between 2 characters or strings :
var str="That s hxt!"; var patt1=/h.t/gi;
document.write(str.match(patt1));
The marked text shows where the expression gets a match

Note : This Modifier finds only hat when the string is " That s hvbfgxt "




This lecture is to be continued ...