Day 2 of 100: Variables — let, const, and Why var Is Dead

Day 2 of 100 — 100 Days of Playwright with TypeScript Challenge. Phase: JavaScript Fundamentals. JavaScript (Days 1-33) → TypeScript (Days 34-63) → Playwright (Days 64-96) → AI Framework Capstone (Days 97-100).

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Variables store test data. Three keywords exist. Only two matter.

let, const, var

const baseUrl = 'https://api.example.com'; // never reassigned
let retryCount = 0;                        // will change
retryCount = 1;                            // fine
// baseUrl = 'x';                          // ERROR: const

// var is function-scoped and hoisted — avoid it
var old = 'do not use';

Rules for Test Code

• Default to const — most test data never changes
• Use let only when reassignment is needed (counters, accumulators)
• Never use var — its scoping causes subtle bugs in loops

// Real test usage
const testUser = { email: 'qa@test.com', password: 'Secret123!' };
let attempts = 0;
while (attempts < 3) { attempts++; }

Tomorrow (Day 3): Data types — strings, numbers, booleans, null, undefined.