Description
Search Terms
preserveConstEnums, const enum, enum
Suggestion
By default all const enum
s are preserved from output. One of the key differences of const enum
s is disallowing to looking up the reversed value:
enum Enum {
Zero,
One,
}
console.log(Enum[1]); // allowed, result is 'One'
const enum ConstEnum {
Zero,
One,
}
console.log(ConstEnum[1]); // Error
This means that we can't access const enum's "reversed" member even if preserveConstEnums
flag is enabled.
JS code of const enum
with enabled preserveConstEnums
is pretty similar to just enum
s right now and contains string literals (even they couldn't be accessed from the code):
var ConstEnum;
(function (ConstEnum) {
ConstEnum[ConstEnum["Zero"] = 0] = "Zero";
ConstEnum[ConstEnum["One"] = 1] = "One";
})(ConstEnum || (ConstEnum = {}));
My feature request is change output of const enum
s when preserveConstEnums
is enabled and strip "reversed" values from it:
var ConstEnum;
(function (ConstEnum) {
ConstEnum["Zero"] = 0;
ConstEnum["One"] = 1;
})(ConstEnum || (ConstEnum = {}));
Note: actually tsc already has similar behaviour if you specify string constant value for every const enum's member, but the values are strings, not numbers - it is kind of workaround if your const enum is used to declare string constants.
Use Cases
Reversed values for const enums are useless and cannot be accessed in the TS code, so why we should emit them? 🤔 I guess in this case the behaviour of const enum
s from types and from execution (JS) purposes will be the same.
Checklist
My suggestion meets these guidelines:
- This wouldn't be a breaking change in existing TypeScript/JavaScript code
- This wouldn't change the runtime behavior of existing JavaScript code
- This could be implemented without emitting different JS based on the types of the expressions
- This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
- This feature would agree with the rest of TypeScript's Design Goals.