🧷 ✅ Most Important String Properties

Property	Description	Example
`length`	Returns number of code units in string	`"hello".length → 5`

🔍 Example:

const str = "Hello 🌍";
console.log(str.length); // 7 → because 🌍 takes 2 code units

🔧 ✅ Most Used String Methods (Grouped by Purpose)

🔹 🔍 1. Searching & Finding

Method	Description	Example
`indexOf(substr)`	First occurrence (case-sensitive)	`"abc".indexOf("b") → 1`
`lastIndexOf()`	Last occurrence	`"ababc".lastIndexOf("b") → 3`
`includes()`	Returns `true/false` if substring found	`"hello".includes("ll")`
`startsWith()`	Checks if string begins with a substring	`"hello".startsWith("he")`
`endsWith()`	Checks if string ends with a substring	`"hello".endsWith("lo")`

🔸 Real Use Case: Validate file extension or detect if URL starts with https.

🔹 ✂️ 2. Extracting & Slicing

Method	Description	Example
`slice(start, end?)`	Extract part of string	`"hello".slice(1,4) → ell`
`substring(start, end?)`	Similar to slice but can't use negatives
`substr(start, length)`	Deprecated, but still seen in old code

🔍 Key Difference (slice vs substring):

"abcdef".slice(-2);      // "ef"
"abcdef".substring(-2);  // "abcdef" → treats negatives as 0

🔹 🛠️ 3. Transforming Case

Method	Description	Example
`toLowerCase()`	Converts to lowercase	`"HELLO".toLowerCase()`
`toUpperCase()`	Converts to uppercase	`"hi".toUpperCase()`

🔹 🧽 4. Cleaning Up Text

Method	Description	Example
`trim()`	Removes spaces from both ends	`" abc ".trim()`
`trimStart()`	Removes leading spaces	`" abc ".trimStart()`
`trimEnd()`	Removes trailing spaces	`" abc ".trimEnd()`

🔹 🧱 5. Modifying & Constructing

Method	Description	Example
`replace(find, replace)`	Replace part of string	`"a-b".replace("-", ":")`
`replaceAll()`	Replaces all matches (ES2021+)	`"a-a".replaceAll("a", "b")`
`repeat(n)`	Repeat string `n` times	`"ha".repeat(3) → "hahaha"`
`padStart(len, str)`	Pads from start to match length	`"7".padStart(2, "0") → "07"`
`padEnd(len, str)`	Pads from end	`"7".padEnd(3, "-") → "7--"`

🔹 🧨 6. Splitting & Joining

Method	Description	Example
`split(sep)`	Splits string into array by separator	`"a,b,c".split(",") → ["a","b","c"]`
`join(sep)`	Joins array into string	`["a","b"].join("-") → "a-b"`

🔸 Real Use Case: CSV processing, word counting, parsing user input.

🔹 🧬 7. Character-Level Access

Method	Description	Example
`charAt(index)`	Returns character at index	`"abc".charAt(1) → b`
`charCodeAt(index)`	UTF-16 code unit value	`"A".charCodeAt(0) → 65`
`at(index)` (ES2022)	Allows negative indexing	`"hello".at(-1) → "o"`

🔸 charAt() is older. Use .at() for cleaner negative-index access.

🔹 🔐 8. Comparison

Method	Description	Example
`localeCompare()`	Locale-sensitive comparison	`"é".localeCompare("e", "en")`
`==`, `===`, `<`	Works lexicographically for strings	`"apple" < "banana"` → true

🧠 Tips to Remember

📌 Mnemonics:

Slice & Dice → slice() helps you "cut out" portions.
Start-End-Include → startsWith(), endsWith(), includes().
TRIM your inputs → always trim() when reading user data.
REPLACE wisely → use replaceAll() for global replacements.
AT your fingertips → use .at() to access characters even from the end.

🎯 Real World Example: Format a Price Input

function formatPrice(input) {
  return input.trim().replace("₹", "").padStart(4, "0");
}
console.log(formatPrice("  ₹45")); // "0045"

🧩 Fun Challenge:

Guess the result:

const str = "123";
console.log(str.padStart(5, "0").repeat(2));

Output: "0012300123" → pad, then repeat

Lesson 8: Mastering JavaScript Strings (PART-2)