javaScript Regex Expression

 javaScript Regex Expression 

A regular expression is a pattern of characters.

The pattern is used to do pattern-matching "search-and-replace" functions on text.

Syntax

/pattern/modifier(s);

Modifiers

Modifiers are used to perform case-insensitive and global searches:

Modifier	Description
g	Perform a global match (find all matches rather than stopping after the first match)
i	Perform case-insensitive matching
m	Perform multiline matching

<p id="demo"></p>

<script>

let text = "Visit W3Schools";

let pattern = /w3schools/i;

let result = text.match(pattern);

document.getElementById("demo").innerHTML = result;

</script>

o/p :- W3Schools

Brackets

Brackets are used to find a range of characters:

Expression	Description
[abc]	Find any character between the brackets
[^abc]	Find any character NOT between the brackets
[0-9]	Find any character between the brackets (any digit)
[^0-9]	Find any character NOT between the brackets (any non-digit)
(x|y)	Find any of the alternatives specified

<p id="demo"></p>

<script>

let text = "Is this all there is?";

let pattern = /[h]/g;

let result = text.match(pattern);

document.getElementById("demo").innerHTML = result;

</script>

o/p- h,h

-------------------------------------------------------------------------------------------------------------------

<p id="demo"></p>

<script>

let text = "Is this all there is?";

let pattern = /[^h]/g;

let result = text.match(pattern);

document.getElementById("demo").innerHTML = result;

</script>

o/p- I,s, ,t,i,s, ,a,l,l, ,t,e,r,e, ,i,s,?

-------------------------------------------------------------------------------------------------------------------

<p id="demo"></p>

<script>

let text = "123456789";

let pattern = /[1-4]/g;

let result = text.match(pattern);

document.getElementById("demo").innerHTML = result;

</script>

o/p:- 1,2,3,4

---------------------------------------------------------------------------------------------------------------

<p id="demo"></p>

<script>

let text = "123456789";

let pattern = /[^1-4]/g;

let result = text.match(pattern);

document.getElementById("demo").innerHTML = result;

</script>

o/p- 5,6,7,8,9

----------------------------------------------------------------------------------------------------------

<p id="demo"></p>

<script>

let text = "re, green, red, green, gren, gr, blue, yellow";

let pattern = /(red|green)/g;

let result = text.match(pattern);

document.getElementById("demo").innerHTML = result;

</script>

o/p - green,red,green

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Metacharacters

Metacharacters are characters with a special meaning:

Metacharacter	Description
.	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, beginning like this: \bHI, end like this: HI\b
\B	Find a match, but not at the beginning/end of a word
\0	Find a NULL character
\n	Find a new line character
\f	Find a form feed character
\r	Find a carriage return character
\t	Find a tab character
\v	Find a vertical tab character
\xxx	Find the character specified by an octal number xxx
\xdd	Find the character specified by a hexadecimal number dd
\udddd	Find the Unicode character specified by a hexadecimal number dddd

Quantifiers

Quantifier	Description
n+	Matches any string that contains at least one n
n*	Matches any string that contains zero or more occurrences of n
n?	Matches any string that contains zero or one occurrences of n
n{X}	Matches any string that contains a sequence of X n's
n{X,Y}	Matches any string that contains a sequence of X to Y n's
n{X,}	Matches any string that contains a sequence of at least X n's
n$	Matches any string with n at the end of it
^n	Matches any string with n at the beginning of it
?=n	Matches any string that is followed by a specific string n
?!n	Matches any string that is not followed by a specific string n

RegExp Object Properties

Property	Description
constructor	Returns the function that created the RegExp object's prototype
global	Checks whether the "g" modifier is set
ignoreCase	Checks whether the "i" modifier is set
lastIndex	Specifies the index at which to start the next match
multiline	Checks whether the "m" modifier is set
source	Returns the text of the RegExp pattern

RegExp Object Methods

Method	Description
compile()	Deprecated in version 1.5. Compiles a regular expression
exec()	Tests for a match in a string. Returns the first match
test()	Tests for a match in a string. Returns true or false
toString()	Returns the string value of the regular expression