NaN and Infinity

The special numeric values NaN and Infinity.

The special numeric values represent "Not a Number" and infinite quantities, following IEEE 754. They model the edge cases of numeric computation — an undefined result, or a value beyond the finite range. Only the Number form supports them; BigInt and Decimal do not.

Syntax

The special values are written as fixed keywords:

specialValue  = nanValue | infinityValue
nanValue      = "NaN"
infinityValue = ["+" | "-"] "Inf"

Structural elements

Token	Name	Description
NaN	Not a Number	An undefined or unrepresentable numeric result
Inf	Infinity	A value beyond the finite range
-	Minus sign	Negative infinity (-Inf)
+	Plus sign	Explicit positive infinity (+Inf); not preserved

Valid forms

NaN                  # Not a Number
Inf                  # positive infinity
-Inf                 # negative infinity
+Inf                 # positive infinity (explicit sign, not preserved)

Not the special value

The special values are case-sensitive and spelled exactly. Any other spelling is not an error — it is simply parsed as an open string (text), so it is not the numeric special value:

nan                  # open string "nan", not NaN
INF                  # open string "INF", not Inf
infinity             # open string "infinity", not Inf
-NaN                 # open string "-NaN" — NaN cannot be signed

To store one of these as a number, write it exactly: NaN, Inf, -Inf, or +Inf. To store the word as text, quote it: "infinity".

Preservation of structure

Internet Object preserves:

• The exact special value written

• The sign of negative infinity

• Syntactic fidelity as written, except that an explicit + sign is not preserved

It does not interpret:

• The operations that produced these values

• Comparison or equality semantics (for example, that NaN equals nothing, including itself)

Those semantics belong to the application.

See Also

• Number — standard floating-point numbers

• Numeric Values — all numeric forms