Holy fuck that is long. When the documentation for the integer parsing function is 10 pages long, there's something seriously wrong with the language

https://en.wikipedia.org/wiki/Principle_of_least_astonishment

...and of course JS made it into the examples, how could it not:

A programming language's standard library usually provides a function similar to the pseudocode ParseInteger(string, radix), which creates a machine-readable integer from a string of human-readable digits. The radix conventionally defaults to 10, meaning the string is interpreted as decimal (base 10). This function usually supports other bases, like binary (base 2) and octal (base 8), but only when they are specified explicitly. In a departure from this convention, JavaScript originally defaulted to base 8 for strings beginning with "0", causing developer confusion and software bugs. This was discouraged in ECMAScript 3 and dropped in ECMAScript 5.

I'd advise to always look into the corresponding documentation before using something from any library.

Okay but this documentation is obviously wrong from the first sentence

The parseInt() function parses a string argument and returns an integer of the specified radix

Integers don't have radices. It should read:

The parseInt() function parses a string argument representing an integer of the specified radix and returns that integer.

~~Either way, I still don't understand the behaviour in the image.~~ nvm, thanks m_f@discuss.online

oh god the reason is even stupider then I expected

Because large numbers use the e character in their string representation (e.g., 6.022e23 for 6.022 × 1023), using parseInt to truncate numbers will produce unexpected results when used on very large or very small numbers. parseInt should not be used as a substitute for Math.trunc().