`parseInt` is not strange

[cD1rtX3]

parseInt only works on strings. When it encounters a number, it has to cast it to a string to work on it. 0.0000005 casts to a string as '5e-7', and so:

1. parseInt encounters the '5' and writes it down.
2. parseInt encounters the 'e' and quits, returning 5.

You could say the same thing about C:

constexpr double d = 5e-7;

char str[snprintf(nullptr, 0, "%lg", d)]; // Makes a buffer big enough
sprintf(str, "%lg", d); // Puts "5e-07" into `str`

const long int l = atol(str);
// `l` is now 5 !???!?!?!?!????!???!1/1/1/1//

You could also say the same about any other language with a parseInt-esque function that works similarly.

Everything is unexpected when you don't understand things.

[cD1rtX3]

The real problem is people using parseInt on numbers. Use Math.trunc instead.

[njt1982]

Are you referring to https://javascriptwtf.com/wtf/parseInt-is-strange ?

If so, I think the WTF is valid; you'd not expect it to simply throw away all the zeros in a number. Maybe if you did parseInt("0.000008", 10)... but as you say, thats because its being cast as a string.

[cD1rtX3]

It doesn't “throw away all the zeros”. It's casting to a string, that string being '5e-7'. The zeros are in the “e-7”.

Like I said, the problem is not with the language, the problem is with people using parseInt on numbers. Don't do that.