Search code examples
javascriptcoercion

Why +true is not equal to true.valueOf?

+true // result: 1

true.valueOf() // result: true

+true === true.valueOf() // result: false

In Javascript Type Coersion, the function called for evaluation is valueOf(). But if the function is called explicity it returns a different value.

Solution

  • the function called for evaluation is valueOf()

    Not always. valueOf() is only meaningful for non-primitive types, since it is defined to return the primitive value of the given object. true by itself is a Boolean primitive and as such calling true.valueOf() would be completely redundant.

    The unary + and - sign operators always return a number by definition. Since a Boolean quite conveniently converts to a number, it only makes sense that +true returns 1.

    There is no reason +true and true.valueOf() should both correspond to the same value.