Regular Expression

Unikaksha: Regular expressions:

a regular expression often refered to as regex, is a sequence of characters that 

forms a searcg pattern. It is a powerful tool for pattern matching and manipulating

of strings in javascript and many other programming languages.

create a regex using two methods:

1) regular expression literal:

involves enclosing the regex pattern between two slashes(/) and using it directly 

in the code.

let regex = /pattern/;

2) regular expression constructor:

let regex = new RegExp("pattern");

literal characters:

literal characters are used to match exact characters or sequence of characters.

1) exact matching:

/abc/ matches the exact sequence of characters "abc".

2) case insensitive matching:

/abc/i - matches the sequence "abc" while ignoring the case.

3) characters matching:

i) /[aeiou]/ - matches any single character in the set "a","e","i","o","u".

ii) /[0-9]/ - matches any digits characters.

iii) /[a-z]/ - matches any lowercase letter.

iv) /[A-Z]/ - matches any uppercase letter.

v) /[^0-9]/ - matches any charcter that is not a digit.

4) escape sequence:

i) /\// - matches a forward slash character ("/").

ii) /\$/ - matches a dollar sign character.

iii) /\\n/ - matches a newline character("\n").

5) unicode characters:

/u{}/ sytax - to specifying the unicode character in regex.

/u{1F600}/ - representing the grinning face emoji.

/u - flag at the end of the regex indicates that it supports unicode characters.

/u{1F600}/u - matches a specific unicode character using its code point.

1)exact matching:

let regex = /abc/;

console.log(regex.test("abc"));

console.log(regex.test("abcd"));

console.log(regex.test("dadbdc"));

console.log(regex.test("ab"));



2) case insentivity:



let regex = /abc/i;

console.log(regex.test("abc"));

console.log(regex.test("Abc"));

console.log(regex.test("ABC"));

console.log(regex.test("aBC"));

console.log(regex.test("aBc"));

console.log(regex.test("aBdC"));

console.log(regex.test("aaBbC"));



3) character matching:

i)



let regex = /[aeiou]/;

console.log(regex.test("apple"));

console.log(regex.test("banana"));

console.log(regex.test("zzzzz"));

ii)



let regex = /[0-9]/;

console.log(regex.test("abc123"));

console.log(regex.test("123"));

console.log(regex.test("a1b2c3d4"));

console.log(regex.test("abc"));



iii)



let regex = /[a-z]/;

console.log(regex.test("abc123"));

console.log(regex.test("123"));

console.log(regex.test("a1b2c3d4"));

console.log(regex.test("ABC"));



iv)

let regex1 = /[A-Z]/;

console.log(regex1.test("abc123"));

console.log(regex1.test("123"));

console.log(regex1.test("a1b2c3d4"));

console.log(regex1.test("abC"));



v)



let regex = /[^0-9]/;

console.log(regex.test("abc123"));

console.log(regex.test("123"));

console.log(regex.test("a1b2c3d4"));

console.log(regex.test("abC"));

console.log(regex.test("!@#$%^&*"));



4) escape charcters:

i) 



let regex = /\//;

console.log(regex.test("http://example.com/"));

console.log(regex.test("http:example.com"));



ii)



let regex = /\$/;

console.log(regex.test("the price is $10"));

console.log(regex.test("the price is 10 dollar"));



iii)



let regex = /\\n/;

console.log(regex.test("New \\n line"));

console.log(regex.test("New Line"));



5) unicode characters:



let regex = /\u{1F600}/u;

console.log(regex.test("hello 😀"));

console.log(regex.test("hello 😁"));



Meta characters: