Which statement accurately describes the difference between null and undefined in JavaScript?

Which statement accurately describes the difference between null and undefined in JavaScript?

• A. Undefined means a variable has been declared but has no value; null is an explicit value assigned to indicate 'no value'. typeof null is 'object' due to a historical quirk.
• B. Undefined means a variable is forcibly null; Null means it has a value but uninitialized.
• C. Undefined and Null are identical in typeof results.
• D. Undefined is used for object properties; Null is used for arrays.

Answer: (A)

Undefined means a variable has been declared but hasn’t been assigned a value yet, while null is an explicit value you assign to indicate that there is intentionally no value. This distinction matters because you can have a variable that is ready to hold something but hasn’t gotten it yet (undefined), whereas null shows that you deliberately emptied or reset the value. A common point to remember is how they behave with typeof. Undefined yields 'undefined', while null yields 'object'—a long-standing quirk in JavaScript that originates from an early representation of objects. This often trips people up, so many developers check for both with a loose comparison (value == null) to catch either case, then use a strict comparison if they need to distinguish them. In practice, you’d use undefined to indicate that something hasn’t been set yet, and null when you want to explicitly mark the absence of a value.

Undefined means a variable has been declared but hasn’t been assigned a value yet, while null is an explicit value you assign to indicate that there is intentionally no value. This distinction matters because you can have a variable that is ready to hold something but hasn’t gotten it yet (undefined), whereas null shows that you deliberately emptied or reset the value.

A common point to remember is how they behave with typeof. Undefined yields 'undefined', while null yields 'object'—a long-standing quirk in JavaScript that originates from an early representation of objects. This often trips people up, so many developers check for both with a loose comparison (value == null) to catch either case, then use a strict comparison if they need to distinguish them.

In practice, you’d use undefined to indicate that something hasn’t been set yet, and null when you want to explicitly mark the absence of a value.