Why is "\n" a number "NaN" in Javascript

Question

In JavaScript on Chrome and Firefox:

isNaN( "\n" ) gives false
parseFloat ( "\n" ) gives NaN

The same is yielded for \t, \r and \f.'

• \n is a number
• Parsed \n gives you Not A Number.
• Escaped characters such as the NULL byte \0, \\ and \" do work as expected.
• We know that NaN is a number, just not representable by any other value
• So \n is a number, that's not representable.

Why do browsers implement it this way?

Answer 1

Because the toNumber conversion of any string that is comprised only of white space (or if it's empty) results in 0.

console.log(Number("\n")); // 0

The parseInt/Float methods actually require some numeric content to be converted, though it'll allow leading spaces, and trailing garbage.

console.log(parseFloat("   123.45odsifjj")); // 123.45

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The toNumber conversion is defined in 9.3.1 ToNumber Applied to the String Type.

A StringNumericLiteral that is empty or contains only white space is converted to +0

Answer 2

This is due to the dynamic typing when you call isNaN. "\n" is not a NaN (a value specified for floats and doubles), "\n" is a string.

EDIT: Apparently, when calling isNaN("\n"), "\n" is converted to a number first using ToNumber which does not have exact same behavior as parseFloat.

However, W3C w3schools says for parseFloat:

If the first character cannot be converted to a number, parseFloat() returns NaN.

This is what causes the asymmetry.