A String in JavaScript is a sequence of characters used to store text.

let course = "JavaScript";

1. String length

Purpose

Returns the total number of characters in a string.

Syntax

string.length

Example

let company = "OpenAI";

console.log(company.length);

Output

6

Real-Time Example

Checking password length before registration.

2. String charAt()

Purpose

Returns the character at a specified index.

Syntax

string.charAt(index)

Example

let city = "Madurai";

console.log(city.charAt(3));

Output

u

Internal Logic

M a d u r a i
0 1 2 3 4 5 6

Index 3 contains "u".

3. String charCodeAt()

Purpose

Returns the Unicode value (UTF-16 code) of a character.

Example

let letter = "A";

console.log(letter.charCodeAt(0));

Output

65

More Examples

console.log("a".charCodeAt(0));

Output:

97

4. String codePointAt()

Purpose

Returns the Unicode code point of a character.

Useful for emojis and special symbols.

Example

let emoji = "😊";

console.log(emoji.codePointAt(0));

Output

128522

Difference

console.log("😊".charCodeAt(0));
console.log("😊".codePointAt(0));

codePointAt() gives the actual Unicode value.

5. String concat()

Purpose

Combines two or more strings.

Example

let firstName = "Annapoorani";
let lastName = " Kadhiravan";

let fullName = firstName.concat(lastName);

console.log(fullName);

Output

Annapoorani Kadhiravan

Alternative

console.log(firstName + lastName);

6. String at()

Purpose

Returns character at a specific position.

Supports negative indexing.

Example

let language = "JavaScript";

console.log(language.at(0));
console.log(language.at(-1));

Output

J
t

7. String [ ]

Purpose

Access characters using bracket notation.

Example

let laptop = "Dell";

console.log(laptop[0]);
console.log(laptop[2]);

Output

D
l

Difference

console.log(laptop.charAt(0));
console.log(laptop[0]);

Both return same result.

8. String slice()

Purpose

Extracts part of a string.

Syntax

string.slice(start,end)

Example

let course = "JavaScript";

console.log(course.slice(0,4));

Output

Java

Negative Index

console.log(course.slice(-6));

Output

Script

9. String substring()

Purpose

Extracts characters between indexes.

Example

let company = "Microsoft";

console.log(company.substring(0,5));

Output

Micro

Difference from slice()

let str = "JavaScript";

console.log(str.slice(-6));
console.log(str.substring(-6));

Output:

Script
JavaScript

substring() doesn't support negative indexes.

10. String substr()

⚠️ Deprecated (Avoid in new projects)

Purpose

Extracts characters based on start position and length.

Example

let city = "Chennai";

console.log(city.substr(2,4));

Output

enna

Explanation

Start at index 2
Take 4 characters

11. String toUpperCase()

Purpose

Converts string to uppercase.

Example

let name = "annapoorani";

console.log(name.toUpperCase());

Output

ANNAPOORANI

12. String toLowerCase()

Purpose

Converts string to lowercase.

Example

let company = "OPENAI";

console.log(company.toLowerCase());

Output

openai

13. String isWellFormed()

Purpose

Checks whether a string contains valid Unicode characters.

Example

let text = "Hello";

console.log(text.isWellFormed());

Output

true

Use Case

Unicode validation before processing text.

14. String toWellFormed()

Purpose

Converts malformed Unicode into valid Unicode.

Example

let text = "\uD800";

console.log(text.toWellFormed());

Output

�

Use Case

Cleaning corrupted text data.

15. String trim()

Purpose

Removes spaces from beginning and end.

Example

let email = "  user@gmail.com  ";

console.log(email.trim());

Output

user@gmail.com

16. String trimStart()

Purpose

Removes spaces only from beginning.

Example

let text = "   Hello";

console.log(text.trimStart());

Output

Hello

17. String trimEnd()

Purpose

Removes spaces only from end.

Example

let text = "Hello   ";

console.log(text.trimEnd());

Output

Hello

18. String padStart()

Purpose

Adds characters at the beginning until desired length.

Example

let orderId = "123";

console.log(orderId.padStart(6,"0"));

Output

000123

Real-Time Example

Generating invoice numbers.

19. String padEnd()

Purpose

Adds characters at the end.

Example

let code = "JS";

console.log(code.padEnd(5,"*"));

Output

JS***

20. String repeat()

Purpose

Repeats a string multiple times.

Example

let star = "*";

console.log(star.repeat(5));

Output

*****

Real-Time Example

Printing separators.

21. String replace()

Purpose

Replaces first matching occurrence.

Example

let sentence = "I love Java. Java is powerful.";

console.log(sentence.replace("Java","JavaScript"));

Output

I love JavaScript. Java is powerful.

Note

Only first occurrence is replaced.

22. String replaceAll()

Purpose

Replaces all matching occurrences.

Example

let sentence = "Java Java Java";

console.log(sentence.replaceAll("Java","JS"));

Output

JS JS JS

23. String split()

Purpose

Converts string into array.

Example

let skills = "HTML,CSS,JavaScript";

let result = skills.split(",");

console.log(result);

Output

["HTML", "CSS", "JavaScript"]

Split by Space

let sentence = "Learning JavaScript Daily";

console.log(sentence.split(" "));

Output

["Learning","JavaScript","Daily"]

Quick Comparison Table

Method	Purpose
length	Count characters
charAt()	Get character
charCodeAt()	Unicode value
codePointAt()	Unicode code point
concat()	Join strings
at()	Access character (supports negative index)
[ ]	Access character
slice()	Extract part of string
substring()	Extract text (no negative index)
substr()	Extract by length (deprecated)
toUpperCase()	Convert to uppercase
toLowerCase()	Convert to lowercase
isWellFormed()	Check valid Unicode
toWellFormed()	Fix invalid Unicode
trim()	Remove spaces both sides
trimStart()	Remove left spaces
trimEnd()	Remove right spaces
padStart()	Add characters at beginning
padEnd()	Add characters at end
repeat()	Repeat string
replace()	Replace first match
replaceAll()	Replace all matches
split()	Convert string to array

References: https://www.w3schools.com/js/js_string_methods.asp