How to compare Enums in TypeScript

typescript enums compare equality
John J. Camilleri picture John J. Camilleri · Sep 30, 2016 · Viewed 57.8k times · Source

In TypeScript, I want to compare two variables containing enum values. Here's my minimal code example:

enum E {
  A,
  B
}

let e1: E = E.A
let e2: E = E.B

if (e1 === e2) {
  console.log("equal")
}

When compiling with tsc (v 2.0.3) I get the following error:

TS2365: Operator '===' cannot be applied to types 'E.A' and 'E.B'.

Same with ==, !== and !=. I tried adding the const keyword but that seems to have no effect. The TypeScript spec says the following:

4.19.3 The <, >, <=, >=, ==, !=, ===, and !== operators

These operators require one or both of the operand types to be assignable to the other. The result is always of the Boolean primitive type.

Which (I think) explains the error. But how can I get round it?

Side note
I'm using the Atom editor with atom-typescript, and I don't get any errors/warnings in my editor. But when I run tsc in the same directory I get the error above. I thought they were supposed to use the same tsconfig.json file, but apparently that's not the case.

Answer

John J. Camilleri picture John J. Camilleri · Sep 30, 2016

Well I think I found something that works:

if (e1.valueOf() === e2.valueOf()) {
  console.log("equal")
}

But I'm a bit surprised that this isn't mentioned anywhere in the documentation.

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