invalid code generated with target "es2015" and "system" modules

[FlorianDold]

The following code

export class MyClass { }

export function myFunction() {
    return new MyClass();
}

is compiled (with tsc test.ts -m system --target es2015) to

System.register([], function(exports_1) {
    "use strict";
    var MyClass;
    function myFunction() {
        return new MyClass();
    }
    exports_1("myFunction", myFunction);
    return {
        setters:[],
        execute: function() {
            class MyClass {
            }
            exports_1("MyClass", MyClass);
        }
    }
});

which is wrong, since the actual definition of MyClass is not in scope of myFunction anymore.

Compiling down to es5 works as expected with respect to the scope of the class.

[jkillian]

Edit: I'm wrong 😄, see #6426 (comment) below

I believe that this is the correct behavior @FlorianDold. When you do export class MyClass { } you are using a class expression instead of a regular class declaration. (Edit: my reasoning here doesn't make any sense, because exporting arbitrary expressions, like export 5, is obviously invalid. There must be an identifier or it must be a default export.) In class expressions, the BindingIdentifier portion (i.e. MyClass) is optional. If provided, as you did, it is only available for use inside of the class body. (See bullet point #2 here).

Instead, you could do something like this:

class MyClass { }
export MyClass;
export function myFunction() {
    return new MyClass();
}

Your original TS code should generate an error, as return new MyClass(); is invalid because MyClass isn't available there. If there's no error, that is a bug most likely.

[weswigham]

export class MyClass { } is still a class declaration (with an export modifier). Our emit is probably wrong - the declaration within the execute function behaves as block scoped (which is normal), but we need to hoist it so its binding is available in the initialization block above. This is probably best done by rewriting the class as a class expression which is assigned to the var made above. (or leaving it as a declaration, but mangling the hoisted name and assigning it to the mangled name)

[jkillian]

Thanks for the correction @weswigham. If you did want to export a named class expression in one statement for some reason, assuming you could do something like export default (class SomeName { });?