🔍 JavaScript typeof Operator – Know What You're Dealing With

Ever wanted to know what kind of value a variable holds in JavaScript?

That’s where the typeof operator comes in. It tells you the type of any value or variable.

But... sometimes it lies. 😅
Let’s break it all down: what typeof gives you, what’s true, what’s weird, and how to handle it.

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✅ The Syntax

typeof value

Returns a string describing the type of the value.

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🔢 1. Numbers

console.log(typeof 42);           // "number"
console.log(typeof 3.14);         // "number"
console.log(typeof NaN);          // "number" ← yes, still a number

✅ Includes both integers, floats, and NaN.

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🔤 2. Strings

console.log(typeof 'hello');      // "string"
console.log(typeof "");           // "string"
console.log(typeof `template`);   // "string"

✅ Works with single, double, and backtick quotes.

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⚙️ 3. Booleans

console.log(typeof true);         // "boolean"
console.log(typeof false);        // "boolean"

✅ Straightforward.

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❓ 4. Undefined

let x;
console.log(typeof x);            // "undefined"
console.log(typeof undefined);    // "undefined"

✅ Default for uninitialized variables.

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🚫 5. Null (🧨 Surprise!)

console.log(typeof null);         // "object"  ❌ (bug in JS since 1995)

🧠 Even though it says "object", null is not an object.

✅ To detect null properly:

value === null;

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📦 6. Objects

console.log(typeof {});           // "object"
console.log(typeof { name: "JS" }); // "object"

✅ Basic objects return "object".

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📋 7. Arrays (still objects!)

console.log(typeof [1, 2, 3]);    // "object" ❌

Array.isArray([1, 2, 3]);         // true ✅

typeof can't distinguish arrays from objects. Use Array.isArray() instead.

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🛠️ 8. Functions

function greet() {}
const arrow = () => {};

console.log(typeof greet);        // "function"
console.log(typeof arrow);        // "function"

✅ The only case where typeof returns "function" — everything else is "object" or primitives.

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🔣 9. Symbols

const sym = Symbol('id');
console.log(typeof sym);          // "symbol"

✅ Unique and immutable — often used as keys.

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🔢 10. BigInt

const big = 1234567890123456789012345678901234567890n;
console.log(typeof big);          // "bigint"

✅ For numbers larger than Number.MAX_SAFE_INTEGER.

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🔄 Summary Table

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🧪 Bonus: typeof vs constructor vs Array.isArray()

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✅ Final Thoughts

• Use typeof for primitive types.

• Use Array.isArray() for arrays.

• Don't trust typeof null — it lies.

• For more complex type checks, use constructor or instanceof.