Explanation of this example is wrong:
https://github.com/denysdovhan/wtfjs#-is-equal-

The abstract equality operator converts both sides to numbers to compare them

This is just wrong. Strings are compared as strings, null compared to undefined is true, to-primitive might return a string instead on number and so on.

Here is how this expression simplifies:

+[] == +![];

First step would be to convert ![] to false because of precedence.