Quick Reference: Conditionals & Logic in JavaScript

1. Strict vs Loose Equality

• === Strict Equality (Checks Value + Type) — Always use this!
• !== Strict Inequality
• == Loose Equality (Coerces Types) — Avoid!

2. The 8 Falsy Values in JavaScript

Only these 8 values evaluate to false in boolean context:

false, 0, -0, 0n, "", null, undefined, NaN.

Everything else is Truthy! (Including [] and {})

3. Logical & Fallback Operators

• && (AND): Short-circuits on first falsy value.
• || (OR): Short-circuits on first truthy value.
• ?? (Nullish Coalescing): Returns right side ONLY if left side is null or undefined. Keeps 0 and ""!
• ? : (Ternary): condition ? ifTrue : ifFalse

4. Clean Code: Guard Clauses Pattern

function processOrder(order) {
  if (!order) return { error: "No order" };
  if (!order.paymentReceived) return { error: "Unpaid" };
  
  // Happy Path
  shipItem(order);
  return { success: true };
}