JS Strings

JavaScript Strings: Immutable Characters, Indexing, & Escape Sequences

Strings are immutable sequences of UTF-16 code units used to represent textual data. In JavaScript, strings can be declared using single quotes ('), double quotes ("), or template literals (`).

String Memory Model & Indexing

flowchart LR
    StringVal["String: 'KodSolution'"] --> Index0["[0]: 'K'"]
    StringVal --> Index1["[1]: 'o'"]
    StringVal --> Index2["[2]: 'd'"]
    StringVal --> Length["length property: 11"]

String Creation Methods Comparison

Practical Code Example

// Demonstrating String properties, character access, and immutability

const siteName = "KodSolution";

// 1. Accessing Characters and Length
console.log(`Site Name Length: ${siteName.length}`); // 11
console.log(`Character at index 0 (bracket): ${siteName[0]}`); // 'K'
console.log(`Character at index 3 (charAt): ${siteName.charAt(3)}`); // 'S'

// 2. Escape Characters
const escapedString = "Line 1
Line 2	Tabbed "Quoted Text" \ Backslash";
console.log("Escaped String Output:
" + escapedString);

// 3. String Immutability Demonstration
let title = "javascript";
title[0] = "J"; // Bracket assignment silently fails on primitives!
console.log(`Title after index assignment attempt: ${title}`); // "javascript" (Unchanged!)

// Correct way: Re-assign a new string
title = title.charAt(0).toUpperCase() + title.slice(1);
console.log(`Corrected Title: ${title}`); // "Javascript"

// 4. Iterating over String Characters
console.log("--- Character Iteration ---");
for (const char of "JS") {
  console.log(`Char: ${char}`);
}

Best Practices & Gotchas

• Strings Are Immutable: Calling string methods (e.g., toLowerCase(), replace()) returns a NEW string; it never mutates the original string.
• Use Template Literals for Dynamic Formatting: Prefer template strings (backticks) over multi-operand + string concatenation.
• UTF-16 Surrogate Pairs: Emoji characters (e.g., 🚀) consist of two UTF-16 code units, so "🚀".length returns 2. Use spread [..."🚀"].length for Unicode-aware character counts.

Self-Check Challenge

Write a function capitalizeFirstLetter(str) that accepts a string and returns the string with its first letter capitalized.