undefined and NaN are not constants. They are global…
““undefined and NaN are not constants. They are global variables, and you can change their values. That should not be possible, and yet it is. Don’t do it.””
About This Quote
This interpretation was drafted with AI assistance. It is one reading of the quote, not the author's own explanation.
NaN and undefined are mutable global variables, contrary to expectations of constant behavior.
In simple terms: These values can be altered, which is unsafe.
Key Takeaway
Never reassign NaN or undefined.
Themes
Programming
JavaScript
variables
Mood
cautionary
technical
Type
best‑practice
warning
When to use this quote
- Code reviews
- static analysis
- team coding standards
Key Concepts
Mutable globals
language design
runtime safety
Questions to Reflect On
- Why were NaN and undefined designed as mutable?
- What safeguards can prevent accidental changes?
A Different Perspective
Changing them can break libraries and cause bugs.