Strings in JavaScript
A string is a sequence of characters used to store text.
You use strings everywhere in JavaScript—for names, messages, inputs, emails, addresses, paragraphs, and more.
Understanding strings is very important because:
Forms handle string input
APIs return text
Searching and filtering require string operations
Error messages, emails, and alerts use strings
Most UI content on webpages is text
In this chapter, you will learn the basics of strings and how to work with them.
What Is a String?
A string is text enclosed in quotation marks.
JavaScript allows three types of quotes:
let name1 = "Aman"; // double quotes
let name2 = 'Riya'; // single quotes
let name3 = `Karan`; // backticks (template literals)
Backticks have special features you will learn later.
Length of a String
Use .length to find how many characters are inside a string.
let word = "JavaScript";
console.log(word.length);
Output:
10
Accessing Characters
Characters in a string have indexes (like arrays).
let city = "Delhi";
console.log(city[0]); // D
console.log(city[1]); // e
Strings Are Immutable
You cannot change a character directly.
let name = "Aman";
name[0] = "R";
console.log(name);
Output:
Aman
Strings can’t be modified like arrays.
Concatenation (Joining Strings)
Method 1: Using +
let first = "Hello";
let second = "World";
let msg = first + " " + second;
console.log(msg);
Output:
Hello World
Method 2: Using template literals (recommended)
Template literals use backticks and ${} for variables.
let name = "Riya";
let greet = `Hello ${name}`;
console.log(greet);
Output:
Hello Riya
Multi-line Strings
Backticks allow writing multi-line text easily.
let paragraph = `
This is line 1
This is line 2
This is line 3
`;
console.log(paragraph);
Useful String Methods
JavaScript has many built-in methods for string operations.
Let’s learn the most commonly used ones.
1. toUpperCase()
console.log("hello".toUpperCase());
Output:
HELLO
2. toLowerCase()
console.log("WELCOME".toLowerCase());
Output:
welcome
3. trim()
Removes unnecessary spaces from start and end.
let text = " JavaScript ";
console.log(text.trim());
Output:
JavaScript
Useful for form input cleaning.
4. includes()
Checks if a word exists inside a string.
let title = "Learn JavaScript";
console.log(title.includes("Java"));
console.log(title.includes("Python"));
Output:
true
false
5. indexOf()
Returns the first index of a character or word.
console.log("banana".indexOf("n"));
Output:
2
If not found ? returns -1
6. slice()
Extracts part of the string.
let word = "JavaScript";
console.log(word.slice(0, 4)); // Java
console.log(word.slice(4)); // Script
7. replace()
Replaces text inside a string.
let msg = "I love JavaScript";
console.log(msg.replace("JavaScript", "Python"));
Output:
I love Python
Real-Life Example: Clean User Input
let username = " aman ";
username = username.trim().toLowerCase();
console.log(username);
Output:
aman
This is very common in login forms.
Real-Life Example: Search Feature
let message = "Welcome to JavaScript learning";
if (message.includes("JavaScript")) {
console.log("Keyword found!");
}
Output:
Keyword found!
Example Program (Complete)
let title = " JavaScript Basics ";
// clean text
title = title.trim();
// show length
console.log("Length:", title.length);
// uppercase and lowercase
console.log(title.toUpperCase());
console.log(title.toLowerCase());
// slicing
console.log(title.slice(0, 10));
// search
console.log(title.includes("Script"));
Output:
Length: 18
JAVASCRIPT BASICS
javascript basics
JavaScript
true
Common Mistakes Beginners Make
Trying to change string characters directly
Forgetting that index begins at 0
Using replace() but expecting it to replace all matches
Confusing slice() with substring()
Forgetting trim() before validating input
Practice Tasks (Do It Yourself)
Create a string and print its length.
Convert your name to uppercase and lowercase.
Slice the first 5 characters of a string.
Check if your city name contains the letter "a".
Clean user input using trim().
Replace one word inside a long sentence.