parseInt() parses number literals with exponent incorrectly

I have just observed that the parseInt function doesn’t take care about the decimals in case of integers (numbers containing the e character).

Let’s take an example: -3.67394039744206e-15

> parseInt(-3.67394039744206e-15)
-3
> -3.67394039744206e-15.toFixed(19)
-3.6739e-15
> -3.67394039744206e-15.toFixed(2)
-0
> Math.round(-3.67394039744206e-15)
0

I expected that the parseInt will also return 0. What’s going on at lower level? Why does parseInt return 3 in this case (some snippets from the source code would be appreciated)?

In this example I’m using node v0.12.1, but I expect same to happen in browser and other JavaScript engines.

Answer

I think the reason is parseInt converts the passed value to string by calling ToString which will return "-3.67394039744206e-15", then parses it so it will consider -3 and will return it.

The mdn documentation

The parseInt function converts its first argument to a string, parses it, and returns an integer or NaN