I know this is for fun, but as general advice to the homies, if a language or system is doing something you didn't expect, make sure to look at the documentation
...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.
But I'm too busy being confused by the behaviors of libraries I previously didn't read the documentation for, to read the documentation for every new library I adopt.
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().