String Short Notes

A String is a sequence of characters used to represent text-based data, such as words, sentences, or symbols. Strings are one of the most commonly used data types in JavaScript and play a key role in handling user input, displaying content, and working with APIs or text files.

String Basics

When you're starting with strings in JavaScript, the first things you'll learn are how to create a string, get specific characters based on their position, and find out how long the string is. These simple concepts might seem small, but they're the building blocks for working with text in almost every JavaScript project.

1. Declaration & Initialization

Strings can be created using single quotes (' '), double quotes (" "), or backticks quotes (` `) in JavaScript.

Example:

let s1 = "GeeksforGeeks"

// Using double Quote
console.log(s1)

let s2 = 'GeeksforGeeks'

// Using Single Quote
console.log(s2)

// using backticks 
console.log(`${s1}`)

GeeksforGeeks
GeeksforGeeks
GeeksforGeeks

2. Finding a letter by its position

Access characters using index (str[i]) or methods like charAt(i).

let str = "JavaScript";

// Using Index
console.log(str[0]); 

// Using charAt() Method 
console.log(str.charAt(1)); 

J
a

3. Finding a length of String

Counting how many characters it contains, including letters, numbers, spaces, and symbols.

let string = "GeeksforGeeks"

console.log(string.length)

13

Now we start Built-in String Method after reading string Basics.

Built-in String Methods

JavaScript string methods are built-in functions that allow you to manipulate, transform, search, and extract information from strings efficiently.

Manipulation

• concat(str2): Combines strings.
• slice(start, end): Extracts a portion (end not included).
• substring(start, end): Similar to slice, but handles negative indices differently.
• replace(search, replacement): Replaces first occurrence of search.
• replaceAll(search, replacement): Replaces all occurrences.

// Define a string variable
let str = "Mind, Power, Soul";

// Use the substring() method to extract a substring 
let part = str.substring(6, 11);

// Output the value of variable
console.log(part);

Power

Transformation

• toUpperCase(), toLowerCase(): Changes case.
• trim(): Removes leading/trailing whitespace.

let str = "  Hello  ";

console.log(str.trim().toUpperCase()); 

HELLO

Searching

• indexOf(subStr): Returns first index of subStr or -1 if not found.
• includes(subStr): Checks if subStr exists (returns boolean).
• startsWith(str), endsWith(str): Checks if string starts/ends with str.

let str = "JavaScript";

console.log(str.indexOf("Script")); 
console.log(str.includes("Java")); 

4
true

Splitting & Joining

• split(separator): Splits string into an array based on separator.
• join(separator): Joins array elements into a string with separator.

let str = "a,b,c";

let arr = str.split(","); // ["a", "b", "c"]
console.log(arr.join("-")); // "a-b-c"

a-b-c

Now we start Operators after reading Built-in String Method.

Operators in JavaScript

In JavaScript, operators are special symbols used to perform actions on values or variables. They're an essential part of how we work with strings, numbers, and other data in a program.

1. Arithmetic Operators

Perform mathematical operations. Often used with numbers but can work with strings in some cases (e.g., concatenation).

• + : Addition (or string concatenation).
• - : Subtraction.
• * : Multiplication.
• / : Division.
• % : Modulus (remainder).

// Addition
let num1 = 10 + 2; 
console.log(num1);

// Substraction
let num2 = 10 - 2; 
console.log(num2);

// multiplication
let num3 = 10*2;
console.log(num3);

// Division
let num4 = 10/2;
console.log(num4);

// Module
let num5 = 10%2;
console.log(num5);

12
8
20
5
0

2. Assignment Operators

Assign values to variables.

• =: Assigns a value.
• += , -= , *= , /= : Combine operation and assignment.

let str = "Hello";
str += " World"; // str = "Hello World"
console.log(str);

Hello World

3. Comparison Operators

Compare value, often used in conditionals. Returns true or false.

• == : Equal (loose equality, converts types).
• === : Strict equal (no type conversion).
• != , !== : Not equal (loose and strict).
• > , < , >= , <= : Greater than, less than.

console.log("5" == 5); // true
console.log("5" === 5); // false

let str = "apple";
console.log(str < "banana"); // true

true
false
true

4. Ternary Operator (?:)

Shorthand for if-else.

let str = "hello";
let result = str.length > 5 ? "True" : "False"; 
console.log(result);

False

5. Typeof Operator

Checks the type of a value.

console.log(typeof "Hello"); // "string"

string

Now we start with some problems on strings after reading Operators.

Some Problems on Strings

Before exploring specific string problems in JavaScript, let’s understand what these problems involve and why they matter. String problems focus on techniques for manipulating and analyzing text, such as checking for palindromes, reversing strings, or compressing data efficiently.

String Reversal

Reverses the characters in a string.

function reverseString(str) {
  return str.split("").reverse().join("");
}
console.log(reverseString("hello"));

olleh

Palindrome Check

Check if String is Palindrome or not.

function isPalindrome(str) {
  // Convert to lowercase and remove non-alphanumeric characters
  str = str.toLowerCase().replace(/[^a-z0-9]/g, "");
  // Compare string with its reverse
  return str === str.split("").reverse().join("");
}


console.log(isPalindrome("A man, a plan, a canal: Panama")); // true
console.log(isPalindrome("race a car")); // false

true
false

Anagram Check

Check if two strings are anagrams.

function isAnagram(str1, str2) {
  str1 = str1.toLowerCase().replace(/[^a-z]/g, "");
  str2 = str2.toLowerCase().replace(/[^a-z]/g, "");
  return str1.split("").sort().join("") === str2.split("").sort().join("");
}

console.log(isAnagram("AMAN" , "MAAN"));