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Const enums are preserved when using transpileModule #5243
Description
It seems that using tsc from command line and calling ts.transpileModule in node provides different results: transpileModule preserves const enums. Whole reproduction source can be found here: https://github.com/mbardauskas/transpile-repro
file enums.d.ts:
declare const enum FooType {
Foo = 1,
Bar = 2,
}
file foo.ts:
/// <reference path="enums.d.ts" />
interface IFoo {
foo: FooType;
}
class FooClass {
public type: FooType;
constructor(obj: IFoo) {
this.type = obj.foo;
}
}
export function test() {
var foo = new FooClass(<IFoo>{
foo: FooType.Foo
});
console.log(foo.type);
}
Using typescript transpileModule to compile file source
var transpiled = ts.transpileModule(inputSource, {
reportDiagnostics: true,
compilerOptions: {
target: ts.ScriptTarget.ES5,
module: ts.ModuleKind.CommonJS,
preserveConstEnums: false
}
});
Output from tsc:
/// <reference path="enums.d.ts" />
var FooClass = (function () {
function FooClass(obj) {
this.type = obj.foo;
}
return FooClass;
})();
function test() {
var foo = new FooClass({
foo: 1 /* Foo */
});
console.log(foo.type);
}
exports.test = test;
Output from transpileModule:
/// <reference path="enums.d.ts" />
var FooClass = (function () {
function FooClass(obj) {
this.type = obj.foo;
}
return FooClass;
})();
function test() {
var foo = new FooClass({
foo: FooType.Foo
});
console.log(foo.type);
}
exports.test = test;
Activity
vladima commentedon Oct 13, 2015
this behavior is by design.
transpileModulegenerally operates on the source code of the single file (in your casefoo.ts) and have not access to other files (enums.d.ts). Because of that for this scenario we don't use type-directed emit because in most cases compiler does not have complete information on hands. I.e. in your case compiler have no idea what is the type ofFooTypeand that FooType.Foo` is actually a const enum and its value should be inlined.More specifically in
transpileModule:constenums are treated as regular enums (even for locally definedconstenums)export\import\requirembardauskas commentedon Oct 13, 2015
Is there a way then to pass
d.tsfiles or source string fortranspileModuleso the const enums would get inlined?vladima commentedon Oct 13, 2015
If multiple files are compiled at once how it is different from normal compilation? You can use minimal compiler sample from the Wiki to see how it can be achieved using compiler API
Add note re const enum to README