JavaScript String Fundamentals

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A string in JavaScript is a sequence of characters used to represent text.

✅ Ways to create strings

let str1 = "Hello";
let str2 = 'World';
let str3 = `Hello World`; // Template literal

String Methods

🔹 1. length

Description: Returns the number of characters in a string.

let str = "Hello";
console.log(str.length); // 5

🔹 2. toUpperCase()

Description: Converts all characters to uppercase.

"hello".toUpperCase(); // "HELLO"

🔹 3. toLowerCase()

Description: Converts all characters to lowercase.

"HELLO".toLowerCase(); // "hello"

🔹 4. trim()

Description: Removes whitespace from both ends.

"  hi  ".trim(); // "hi"

🔹 5. trimStart() / trimEnd()

Description: Removes whitespace from start or end only.

"  hi".trimStart(); // "hi"
"hi  ".trimEnd();   // "hi"

🔹 6. includes(substring)

Description: Checks if string contains a substring → returns true/false.

"JavaScript".includes("Script"); // true

🔹 7. startsWith()

Description: Checks if string starts with given value.

"Hello".startsWith("He"); // true

🔹 8. endsWith()

Description: Checks if string ends with given value.

"Hello".endsWith("lo"); // true

🔹 9. indexOf()

Description: Returns first index of substring, or -1 if not found.

"Hello".indexOf("l"); // 2

🔹 10. lastIndexOf()

Description: Returns last occurrence index.

"Hello".lastIndexOf("l"); // 3

🔹 11. slice(start, end)

Description: Extracts part of string (supports negative index).

"JavaScript".slice(0, 4); // "Java"
"Hello".slice(-2); // "lo"

🔹 12. substring(start, end)

Description: Similar to slice() but does not accept negative index.

"JavaScript".substring(4, 10); // "Script"

🔹 13. substr(start, length) ⚠️ Deprecated

Description: Extracts substring using length (not recommended now).

"Hello".substr(1, 3); // "ell"

🔹 14. replace(search, value)

Description: Replaces first match.

"Hello World".replace("World", "JS"); // "Hello JS"

🔹 15. replaceAll()

Description: Replaces all occurrences.

"a-b-c".replaceAll("-", ","); // "a,b,c"

🔹 16. split(separator)

Description: Converts string into array.

"a,b,c".split(","); // ["a", "b", "c"]

🔹 17. concat()

Description: Joins two or more strings.

"Hello".concat(" ", "World"); // "Hello World"

🔹 18. charAt(index)

Description: Returns character at given index.

"Hello".charAt(1); // "e"

🔹 19. charCodeAt(index)

Description: Returns Unicode value of character.

"A".charCodeAt(0); // 65

🔹 20. repeat(n)

Description: Repeats string n times.

"Hi ".repeat(3); // "Hi Hi Hi "

🔹 21. padStart(length, char)

Description: Pads string from start.

"5".padStart(3, "0"); // "005"

🔹 22. padEnd(length, char)

Description: Pads string from end.

"5".padEnd(3, "0"); // "500"

🔹 23. match(regex)

Description: Returns matches based on regex.

"abc123".match(/\d+/); // ["123"]

🔹 24. matchAll(regex)

Description: Returns all matches (iterator).

[..."a1b2".matchAll(/\d/g)]; // ["1", "2"]

🔹 25. search(regex)

Description: Returns index of first match.

"hello123".search(/\d/); // 5

🔹 26. localeCompare()

Description: Compares two strings (useful for sorting).

"a".localeCompare("b"); // -1

🔹 27. normalize()

Description: Normalizes Unicode characters.

"é".normalize();

🔹 28. valueOf()

Description: Returns primitive string value.

let str = new String("hello");
str.valueOf(); // "hello"

🔹 29. toString()

Description: Converts object to string.

let str = new String("hello");
str.toString(); // "hello"

🔹 30. Template Literals (`)

Description: Allows interpolation and multi-line strings.

let name = "John";
console.log(`Hello ${name}`);

⚡ Quick Categorization

🔍 Search Methods

  • includes(), indexOf(), search()

✂️ Extract Methods

  • slice(), substring(), substr()

🔄 Modify Methods

  • replace(), replaceAll(), trim()

🔧 Utility Methods

  • split(), concat(), repeat()

🔡 Case Methods

  • toUpperCase(), toLowerCase()

🔥 20 JavaScript String Programs (with Solutions)

✅ 1. Reverse a string

let str = "hello";
let reversed = str.split("").reverse().join("");
console.log(reversed);

✅ 2. Check palindrome

let str = "madam";
let result = str === str.split("").reverse().join("");
console.log(result);

✅ 3. Count vowels

let str = "hello";
let count = str.match(/[aeiou]/gi)?.length || 0;
console.log(count);

✅ 4. Count consonants

let str = "hello";
let count = str.match(/[^aeiou]/gi).length;
console.log(count);

✅ 5. Remove spaces

let str = "h e l l o";
console.log(str.replaceAll(" ", ""));

✅ 6. Convert first letter to uppercase

let str = "hello";
console.log(str.charAt(0).toUpperCase() + str.slice(1));

✅ 7. Find longest word

let str = "I love JavaScript programming";
let words = str.split(" ");
let longest = words.reduce((a, b) => a.length > b.length ? a : b);
console.log(longest);

✅ 8. Count words

let str = "Hello world JS";
console.log(str.split(" ").length);

✅ 9. Check substring exists

let str = "JavaScript";
console.log(str.includes("Script"));

✅ 10. Replace all vowels with *

let str = "hello";
console.log(str.replace(/[aeiou]/gi, "*"));

✅ 11. Convert string to array

let str = "hello";
console.log(str.split(""));

✅ 12. Remove duplicate characters

let str = "aabbcc";
let unique = [...new Set(str)].join("");
console.log(unique);

✅ 13. Count character frequency

let str = "hello";
let obj = {};
for (let ch of str) {
  obj[ch] = (obj[ch] || 0) + 1;
}
console.log(obj);

✅ 14. Check anagram

let a = "listen";
let b = "silent";let result = a.split("").sort().join("") === b.split("").sort().join("");
console.log(result);

✅ 15. Capitalize each word

let str = "hello world";
let result = str.split(" ").map(w => w.charAt(0).toUpperCase() + w.slice(1)).join(" ");
console.log(result);

✅ 16. Extract numbers from string

let str = "abc123xyz";
console.log(str.match(/\d+/)[0]);

✅ 17. Check if string contains only digits

let str = "12345";
console.log(/^\d+$/.test(str));

✅ 18. Repeat string N times

let str = "hi";
console.log(str.repeat(3));

✅ 19. Truncate string

let str = "JavaScript";
console.log(str.slice(0, 4));

✅ 20. Convert string to title case

let str = "javascript is fun";
let result = str.split(" ")
  .map(w => w[0].toUpperCase() + w.slice(1))
  .join(" ");
console.log(result);

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