JavaScript Regex – Important Regular Expressions You need to Know

Parsing and extracting data from text or validating texts to a specific pattern is an important requirement in programming. JavaScript uses regular expressions to describe a pattern of characters. This JavaScript Regex article will list out the different methods of using expressions in the following sequence:

• What are Regular Expressions?
• JavaScript Regex
• Modifiers
• Brackets
• Metacharacters
• Quantifiers
• Object Properties
• Methods

What are Regular Expressions?

A Regular Expression is a sequence of characters that constructs a search pattern. When you search for data in a text, you can use this search pattern to describe what you are looking for.

A regular expression can be a single character or a more complicated pattern. It can be used for any type of text search and text replace operations. A Regex pattern consist of simple characters, such as /abc/, or a combination of simple and special characters, such as /ab*c/ or  /example(d+).d*/.

JavaScript Regex

In JavaScript, a regular expression is an object that describes a pattern of characters. The JavaScript RegExp class represents regular expressions, and both String and RegExp define methods. It uses regular expressions to perform pattern-matching and search-and-replace functions on text.

Syntax:

A regular expression is defined with the RegExp () constructor as:

var pattern = new RegExp(pattern, attributes);

or simply

var pattern = /pattern/attributes;

Here,

• Pattern – A string that specifies the pattern of the regular expression or another regular expression.
• Attributes – An optional string containing attributes that specify global, case-insensitive, and multi-line matches.

There are different methods of using JavaScript Regex. So let’s move ahead and have a look at the different expressions.

Modifiers

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

Let’s take an example and see how these modifiers are used in JavaScript.

g modifier:

let str = "This is the example";
let pattern = /is/g;

Output:

is,is

i modifier:

let str = "Welcome to Edureka";
let pattern = /edureka/i;

Output:

Edureka

m modifier:

var str = "nthe dog ran after nthe cat";
var patt1 = /^the/m;

Output:

the

Brackets

Brackets are used to find a range of characters.

Example:

var str = "Edureka Online 123";
var ex1 = /[e]/gi;    //[abc]
var ex2 = /[^e]/gi;   //[^abc]
var ex3 = /[2]/g;      //[0-9]
var ex4 = /[^2]/g;     //[^0-9]

Output:

E,e,e
d,u,r,k,a,O,n,l,i,n,1,2,3
2
E,d,u,r,e,k,a,O,n,l,i,n,e,1,3

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Metacharacters

Metacharacters are characters with a special meaning.

Let’s take an example to see how these metacharacters are used:

var str = "100% Genuine";
var pattern1 = /w/g;
var pattern2 = /W/g;
var pattern2 = /d/g;
var pattern2 = /D/g;
var pattern2 = /s/g;
var pattern2 = /S/g;

Output:

1,0,0,G,e,n,u,i,n,e
%
1,0,0
%,G,e,n,u,i,n,e

1,0,0,%,G,e,n,u,i,n,e

Quantifiers

Let’s take an example to see how these Quantifiers are used:

var str = "Hello, welcome to edureka! 1 12 123";
var quant1 = /e+/g;
var quant2 = /el*/g;
var quant3 = /1?/g;
var quant4 = /d{2}/g;

Output:

e,e,e,e,e
ell,el,e,e,e
,,,,,,,,,,,,,,,,,,,,,,,,,,,1,,1,,,1,,,
12,12

Object Properties

Let’s take an example to see how these object properties are used:

var pattern1 = new RegExp("Welcome to Edureka", "g");
var result1 = pattern1.constructor;
var str = "Hello World!";
var pattern2 = /Wor/g;
var result2 = pattern2.global;
var pattern3 = /hel/i;
var result3 = pattern3.ignoreCase;

Output:

function RegExp() { [native code] }
true
true

Object Methods

exec() method:

var str = "Edureka online courses";
var method1 = new RegExp("e");
var result = method1.exec(str);

Output:

e

test() method:

var str = "Edureka online courses";
var method1 = new RegExp("e");
var result = method1.exec(str);

Output:

true

toString() method:

<span>var method2 = new RegExp("Welcome to edureka", "g");</span>
<span>var result = method2.toString();</span>

Output:

/Welcome to edureka/g

These were some of the different methods to define JavaScript Regex. With this, we have come to the end of our article. I hope you understood what are JavaScript Regex and the different methods to define expressions.

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