Overview of Strings

In JavaScript, a string is a primitive data type used to represent a sequence of characters (text). Strings can be enclosed in single quotes (''), double quotes (""), or backticks (`) for template literals. They are immutable, meaning any operation on a string creates a new string rather than modifying the original. Strings are widely used for storing and manipulating text, such as user input, messages, or data.

Represented internally as UTF-16 encoded sequences of characters.
Can include letters, numbers, symbols, and special characters (e.g., emojis).
Immutable: Operations like toUpperCase() or replace() return new strings.
Accessible as array-like structures using indices (e.g., str[0]).

String Creation

Strings can be created in three ways:

Single Quotes:

let str = 'Hello';

Double Quotes:

let str = "World";

Template Literals (ES6+, using backticks):

let str = `Hello, World!`;

Common String Methods

JavaScript provides a rich set of built-in methods for string manipulation. Some commonly used methods include:

Length:

Returns the number of characters in a string (property, not a method).

"Hello".length; // 5

Case Conversion:

"Hello".toUpperCase(); // "HELLO"
"World".toLowerCase(); // "world"

Trimming:

"  Hello  ".trim();      // "Hello"
"  Hello".trimStart();    // "Hello"
"Hello  ".trimEnd();      // "Hello"

Substring Extraction:

"Hello World".slice(0, 5);       // "Hello"
"Hello World".substring(6, 11);  // "World"

Replace:

"Hello World".replace("World", "Universe");  // "Hello Universe"
"Hi Hi".replaceAll("Hi", "Hey");            // "Hey Hey"

Splitting and Joining:

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

Character Access:

"Hello".charAt(0);         // "H"
"Hello"[0];                // "H"
"Hello".charCodeAt(0);     // 72

Concatenation:

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

Padding:

"5".padStart(3, "0"); // "005"
"5".padEnd(3, "0");   // "500"

Repeating:

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

String Search & Manipulation

Search Methods:

"Hello World".indexOf("World");      // 6
"Hello Hello".lastIndexOf("Hello");  // 6
"Hello World".includes("World");     // true
"Hello World".startsWith("Hello");   // true
"Hello World".endsWith("World");     // true

Regular Expression Methods:

"Hello123".match(/\\d+/);                 // ["123"]
"Hello World".search(/\\s/);              // 5
"Hello World".replace(/\\s/g, "-");       // "Hello-World"

String Template

String Template (ES6+) use backticks (`) and allow:

Multi-line strings
Expression interpolation using ${}
Tagged templates for custom processing

let name = "World";
let greeting = `Hello, ${name}!`;  // "Hello, World!"
let multiLine = `Line 1
Line 2`;                           // Preserves line breaks
let a = 5, b = 10;
let sum = `Sum: ${a + b}`;         // "Sum: 15"

// Tagged template
function tag(strings, ...values) {
  return strings[0] + values[0].toUpperCase();
}
tag`Hello, ${name}!`; // "Hello, WORLD!"

String Reference

Operation	Method/Property/Example
Length	`str.length` → `"Hello".length` → 5
Uppercase	`toUpperCase()` → `"hello".toUpperCase()` → "HELLO"
Lowercase	`toLowerCase()` → `"WORLD".toLowerCase()` → "world"
Trim	`trim()` → `" Hello ".trim()` → "Hello"
Substring	`slice(start,end)` → `"Hello World".slice(0,5)` → "Hello"
Replace	`replace(search,new)` → `"Hi".replace("Hi","Hey")` → "Hey"
Split	`split(sep)` → `"a,b".split(",")` → ["a","b"]
Join (array)	`array.join(sep)` → `["a","b"].join("-")` → "a-b"
Find Index	`indexOf(sub)` → `"Hello".indexOf("l")` → 2
Check Substring	`includes(sub)` → `"Hello".includes("lo")` → true
Character Access	`charAt(idx)` or `str[idx]` → `"Hello"[0]` → "H"
Concatenate	`concat(str)` or `+` → `"Hello" + " World"` → "Hello World"
Padding	`padStart(len,pad)` → `"5".padStart(3,"0")` → "005"
Repeat	`repeat(count)` → `"Hi".repeat(2)` → "HiHi"
String Template	`Hello, ${expr}` → `Hi, ${"World"}` → "Hi, World"