Typescript says types a and b have no overlap What does it mean

Question

const value = Math.random() < 0.5 ? "a" : "b";
if (value !== "a") {
  // ...
} else if (value === "b") {
This condition will always return 'false' since the types '"a"' and '"b"' have no overlap.

  // Oops, unreachable
}

Found this code in a tutorial. I want to understand the meaning of this error: "types '"a"' and '"b"' have no overlap."

What are they talking about?

Answer 1

Love the fact that when I finally find somebody with the same bug, there are no suggested fixes... WTF is this, suddenly the values are read as types???

Answer 2

In this case I guess this means that since value is either "a" or "b" and the first validation checks if value is not "a", it means that it will enter the first block of code when it's "b", so it will never enter the second block. I guess you meant to write if (value === a){something } else {something else}.