JS undefined
Undefined often means a value was not supplied or a property was not found. Distinguish that from a deliberate null value.
Where to run this
This example uses the JavaScript console playground. Select Run to execute it; the example does not run on this lesson page.
A practical example
const session = {title: "Repair club"};
console.log(session.price === undefined);
What happens
The missing price property reads as undefined.