String

Welcome to the String section of JDCodebase! Strings are a fundamental data type used to represent sequences of characters. Many interview problems are based on efficient string manipulation, pattern matching, and transformation.

What You’ll Learn

Basic string manipulation: concatenation, slicing, length
Two-pointer and sliding window approaches
Reversing, capitalizing, and formatting strings
Checking palindromes, anagrams, and patterns
Working with character frequency and hashing

JavaScript String Methods

str.length: Returns the length of the string.

Before: "hello".length
Code: str = "hello"; str.length;
After: 5

str.charAt(index): Returns the character at the specified index.

Before: "hello"
Code: str.charAt(1);
After: "e"

str.slice(start, end): Extracts a section of the string and returns it.

Before: "hello world"
Code: str.slice(0, 5);
After: "hello"

str.substring(start, end): Returns the substring between two indexes.

Before: "hello world"
Code: str.substring(6);
After: "world"

str.toUpperCase(): Converts the string to uppercase letters.

Before: "hello"
Code: str.toUpperCase();
After: "HELLO"

str.toLowerCase(): Converts the string to lowercase letters.

Before: "HELLO"
Code: str.toLowerCase();
After: "hello"

str.includes(substr): Checks if a substring exists within the string.

Before: "hello world"
Code: str.includes("world");
After: true

str.replace(old, new): Replaces part of the string with another string.

Before: "Hello World"
Code: str.replace("World", "JS");
After: "Hello JS"

str.split(delimiter): Splits the string into an array by delimiter.

Before: "a,b,c"
Code: str.split(",");
After: ["a", "b", "c"]

str.trim(): Removes whitespace from both ends of the string.

Before: "  hello  "
Code: str.trim();
After: "hello"

Try This Example

Check if a string is a palindrome.

function isPalindrome(str) {
    let left = 0;
    let right = str.length - 1;
    while (left < right) {
      if (str[left] !== str[right]) return false;
      left++;
      right--;
    }
    return true;
  }

Input: "racecar"

Expected Output: true