Truthy, Falsy, and Type Coercion in JavaScript: Avoid Bugs with Clear Logical Evaluations

1️⃣ What Are Truthy and Falsy Values?

In JavaScript, every value is either truthy or falsy when evaluated in a boolean context (like if, while, &&, ||, !).

🔸 Falsy Values (Only 7):

false
0
-0
0n        // BigInt zero
""        // empty string
null
undefined
NaN

Everything else is truthy — including empty arrays [], empty objects {}, and even "0".

if ("0") console.log("Truthy"); // 
if ([]) console.log("Truthy"); // 

2️⃣ Type Coercion in JavaScript: Implicit and Explicit

Type coercion is the automatic (or implicit) conversion of values from one data type to another.

🔹 Implicit Coercion

"5" + 1        // "51"  → string
"5" - 1        // 4     → number
true + 1       // 2
false == 0     // true (⚠️)

🔹 Explicit Coercion

Number("5")     // 5
String(100)     // "100"
Boolean("")     // false

✅ Use explicit coercion for clarity and safety.

3️⃣ Equality: == vs ===

• == → Loose equality (with coercion)

• === → Strict equality (no coercion)

0 == false      // true (⚠️)
0 === false     // false

"" == false     // true (⚠️)
"" === false    // false

✅ Always use === unless you have a strong reason not to.

4️⃣ Logical Operators and Double Negation

Logical operators convert values to boolean when necessary.

🔹 OR (||)

Returns the first truthy value

const name = user.name || "Guest";

🔹 AND (&&)

Returns the first falsy value

const isLoggedIn = user && user.isActive;

🔹 Double NOT (!!)

Converts any value to a strict boolean:

!!"hello"       // true
!!0             // false
!![]            // true


5️⃣ Real-World Use Cases and Pitfalls
✅ Default values with OR:
function greet(name) {
  const userName = name || "Guest";
  console.log("Hello, " + userName);
}

✅ Optional chaining + AND:
const email = user && user.contact && user.contact.email;

❌ Common Pitfall:
false || "value"  // returns "value", but what if false is valid?

✅ Prefer nullish coalescing (??) for better safety:
false ?? "default"  // false ✅
null ?? "default"   // "default"

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