JavaScript String Methods

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

let course = "JavaScript";

Returns the total number of characters in a string.

string.length
js
let company = "OpenAI";

console.log(company.length);
6

Checking password length before registration.

Returns the character at a specified index.

string.charAt(index)
js
let city = "Madurai";

console.log(city.charAt(3));
u
M a d u r a i
0 1 2 3 4 5 6

Index 3 contains "u".

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

let letter = "A";

console.log(letter.charCodeAt(0));
65
console.log("a".charCodeAt(0));

Output:

97

Returns the Unicode code point of a character.

Useful for emojis and special symbols.

let emoji = "😊";

console.log(emoji.codePointAt(0));
128522
console.log("😊".charCodeAt(0));
console.log("😊".codePointAt(0));

codePointAt()

gives the actual Unicode value.

Combines two or more strings.

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

let fullName = firstName.concat(lastName);

console.log(fullName);
Annapoorani Kadhiravan
console.log(firstName + lastName);

Returns character at a specific position.

Supports negative indexing.

let language = "JavaScript";

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

Access characters using bracket notation.

let laptop = "Dell";

console.log(laptop[0]);
console.log(laptop[2]);
D
l
console.log(laptop.charAt(0));
console.log(laptop[0]);

Both return same result.

Extracts part of a string.

string.slice(start,end)
js
let course = "JavaScript";

console.log(course.slice(0,4));
Java
console.log(course.slice(-6));
Script

Extracts characters between indexes.

let company = "Microsoft";

console.log(company.substring(0,5));
Micro
js
let str = "JavaScript";

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

Output:

Script
JavaScript

substring()

doesn't support negative indexes.

⚠️ Deprecated (Avoid in new projects)

Extracts characters based on start position and length.

let city = "Chennai";

console.log(city.substr(2,4));
enna
Start at index 2
Take 4 characters

Converts string to uppercase.

let name = "annapoorani";

console.log(name.toUpperCase());
ANNAPOORANI

Converts string to lowercase.

let company = "OPENAI";

console.log(company.toLowerCase());
openai

Checks whether a string contains valid Unicode characters.

let text = "Hello";

console.log(text.isWellFormed());
true

Unicode validation before processing text.

Converts malformed Unicode into valid Unicode.

let text = "\uD800";

console.log(text.toWellFormed());
�

Cleaning corrupted text data.

Removes spaces from beginning and end.

let email = "  user@gmail.com  ";

console.log(email.trim());
user@gmail.com

Removes spaces only from beginning.

let text = "   Hello";

console.log(text.trimStart());
Hello

Removes spaces only from end.

let text = "Hello   ";

console.log(text.trimEnd());
Hello

Adds characters at the beginning until desired length.

let orderId = "123";

console.log(orderId.padStart(6,"0"));
000123

Generating invoice numbers.

Adds characters at the end.

let code = "JS";

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

Repeats a string multiple times.

let star = "*";

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

Printing separators.

Replaces first matching occurrence.

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

console.log(sentence.replace("Java","JavaScript"));
I love JavaScript. Java is powerful.

Only first occurrence is replaced.

Replaces all matching occurrences.

let sentence = "Java Java Java";

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

Converts string into array.

let skills = "HTML,CSS,JavaScript";

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

console.log(result);
["HTML", "CSS", "JavaScript"]
js
let sentence = "Learning JavaScript Daily";

console.log(sentence.split(" "));
["Learning","JavaScript","Daily"]

References:

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