[1] In JavaScript, other values are automcatically converted into true and false according to conversion rules, but we choose not to make use of these conversion rules in this book.
[2] For an expression of the form a (b > 0 ? + : -) b the JavaScript interpreter would not know the precedence of the operator between a and b, and therefore such expressions are not allowed.
1.1.6 Conditional Expressions and Predicates