JavaScript String Methods

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

let course = "JavaScript";

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1. String length

Purpose

Returns the total number of characters in a string.

Syntax

string.length

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Example

let company = "OpenAI";

console.log(company.length);

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Output

6

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Real-Time Example

Checking password length before registration.

2. String charAt()

Purpose

Returns the character at a specified index.

Syntax

string.charAt(index)

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Example

let city = "Madurai";

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

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Output

u

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Internal Logic

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

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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));

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Output

65

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More Examples

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

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Output:

97

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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));

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Output

128522

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Difference

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

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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);

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Output

Annapoorani Kadhiravan

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Alternative

console.log(firstName + lastName);

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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));

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Output

J
t

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7. String [ ]

Purpose

Access characters using bracket notation.

Example

let laptop = "Dell";

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

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Output

D
l

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Difference

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

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Both return same result.

8. String slice()

Purpose

Extracts part of a string.

Syntax

string.slice(start,end)

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Example

let course = "JavaScript";

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

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Output

Java

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Negative Index

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

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Output

Script

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9. String substring()

Purpose

Extracts characters between indexes.

Example

let company = "Microsoft";

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

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Output

Micro

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Difference from slice()

let str = "JavaScript";

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

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Output:

Script
JavaScript

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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));

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Output

enna

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Explanation

Start at index 2
Take 4 characters

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11. String toUpperCase()

Purpose

Converts string to uppercase.

Example

let name = "annapoorani";

console.log(name.toUpperCase());

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Output

ANNAPOORANI

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12. String toLowerCase()

Purpose

Converts string to lowercase.

Example

let company = "OPENAI";

console.log(company.toLowerCase());

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Output

openai

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13. String isWellFormed()

Purpose

Checks whether a string contains valid Unicode characters.

Example

let text = "Hello";

console.log(text.isWellFormed());

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Output

true

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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());

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Output

�

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Use Case

Cleaning corrupted text data.

15. String trim()

Purpose

Removes spaces from beginning and end.

Example

let email = "  [email protected]  ";

console.log(email.trim());

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Output

[email protected]

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16. String trimStart()

Purpose

Removes spaces only from beginning.

Example

let text = "   Hello";

console.log(text.trimStart());

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Output

Hello

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17. String trimEnd()

Purpose

Removes spaces only from end.

Example

let text = "Hello   ";

console.log(text.trimEnd());

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Output

Hello

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18. String padStart()

Purpose

Adds characters at the beginning until desired length.

Example

let orderId = "123";

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

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Output

000123

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Real-Time Example

Generating invoice numbers.

19. String padEnd()

Purpose

Adds characters at the end.

Example

let code = "JS";

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

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Output

JS***

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20. String repeat()

Purpose

Repeats a string multiple times.

Example

let star = "*";

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

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Output

*****

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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"));

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Output

I love JavaScript. Java is powerful.

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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"));

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Output

JS JS JS

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23. String split()

Purpose

Converts string into array.

Example

let skills = "HTML,CSS,JavaScript";

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

console.log(result);

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Output

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

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Split by Space

let sentence = "Learning JavaScript Daily";

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

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Output

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

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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