explanation of https://twitter.com/#!/angusTweets/status/130767521417662464

toprimitive thing

Also not that `a + "a"` is "3a" (and "a3" the other way around)

I'm pretty certain it's because `typeof a === "object"` and `typeof "a" === "string"`.

The `+` operator calls `toPrimitive` on each operand, but since the literal strings
are already primitives, no further action is taken.  It's only when they are
objects that it delegates to `[[DefaultValue]]` which ends up calling its `valueOf` method.