What is "undefined"

A variable is undefined if it has not been assigned a value.

Depending on the programming language in question, undefined may be a real value or a default value may have been set to "" (an empty string), 0 or NULL anyway.

Access to the indefinite variable may result in some kind of error condition.

Useful links

• MDN - undefined javascript

We have questions here that we can consider as canonical and reading them will learn a lot of what you need to solve your problem:

• How to check Undefined correctly in Javascript
• (reserved for the community to add)