Truthy & Falsy Values

Definition

In JavaScript, every value has an inherent boolean 'truthiness'. When evaluated in a boolean context (like an `if` statement), values are coerced to either `true` or `false`.

Explain Like I'm New

Imagine a nightclub bouncer asking 'Are you a real value?'. Almost everyone gets in (Truthy). But there is a strict blacklist of exactly 6 values that are rejected at the door (Falsy).

Real World Example

Checking if an array exists before mapping it: `if (users) { users.map(...) }` instead of checking `if (users !== undefined && users !== null)`.

Common Use Cases

•Short-circuit evaluation
•Simplified if-statements

Interactive Example

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Interview Questions

basic

What are the 6 falsy values in JavaScript?

intermediate

Is an empty array `[]` truthy or falsy?

advanced

What is `document.all` and why is it falsy?

Flash Cards

Question

What are the 6 falsy values?

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Answer

`false`, `0`, `""` (empty string), `null`, `undefined`, and `NaN`. (Technically `0n` BigInt and `document.all` are also falsy).

Question

Is an empty array truthy or falsy?

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Answer

It is Truthy! In JavaScript, ALL objects and arrays are truthy, even if they are empty. To check if an array is empty, you must check its length: `if (arr.length > 0)`.