Observe null and undefined

Compare the historical typeof results for null and undefined.

Official sourceECMAScript — undefined and null valuesReviewed: 2026-08-26

STEP 1 · LEARN

How it works

undefined is used when a binding has no assigned value yet. null is an intentional primitive value; however, for historical reasons, typeof null returns “object”.

Correct example

const emptyValue = null;
let pending;
console.log(typeof emptyValue);
console.log(typeof pending);

The two lines show the real behaviour: object for null and undefined for the uninitialized binding.

Common mistake

const emptyValue = 'null';
let pending = 'undefined';

The texts “null” and “undefined” are strings, not the corresponding primitive values.

STEP 2 · APPLY

Your exercise

Declare emptyValue as null and pending without a value; print typeof for both in that order.

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STEP 4 · CHECK

What needs to pass

0%not checked

emptyValue is declared with const and null.
The source applies typeof to both variables.
The output is object, then undefined.

Explain the solution logic

The declarations create distinct values, and typeof reveals both the difference and the historical null exception.

How it works

Your exercise

Write and run the code

What needs to pass