includes support for IE 9+

A very simple workaround is

var array = [1, 2, 3];
array.indexOf(1) !== -1;
// → true

[markogresak]

@IonicaBizau I do not know why would that be simpler, other than in number of characters used. The readability of this code is bad and might even be confusing for people who do not know about unary operators and how bitwise negation works, which is especially true for new programmers. Performance wise, there is next to none difference.

[stevenvachon]

Some features, such as Object.assign, have a rule despite having no implementation in IE. I think that this issue can be closed.