Confusing behaviour with basic type boolean in TypeScript

Question

From TypeScript webpage: \"The most basic datatype is the simple true/false value, which JavaScript and TypeScript call a boolean value.\"

Ok so far so good, it\'s just

Answer 1

See https://github.com/Microsoft/TypeScript/issues/11178#issuecomment-249877718

This is working as intended. The compiler performs control flow analysis and knows that p has the actual value Place.Left where you're performing the === operations, and it is calling out that it makes no sense to compare a value that is known to be Place.Left to a value that is known to be Place.Right. It's effectively like writing Place.Left === Place.Right or 1 === 2, both of which would also produce errors.

You get the error message because TypeScript also warns about possible developer errors. As you set a to false (and never change it), it makes no sense to check for a == true as that is never true in your code. Essentially, TypeScripts warns you about dead code.