__createBinding assumes exports are readonly

Using tslib 1.12.0, we are seeing the following error being thrown:

TypeError: Cannot set property foo of #<Object> which has only a getter

This is a result of this commit, which changes __exportStar to use __createBinding, which now uses Object.defineProperty to create a readonly property on exports.

The implication is that it’s no longer possible to do this in TypeScript:

# module1
export function foo() { /* do something */ }

# module2
export * from 'module1';
export function foo() { /* do another thing */ }

This differs from CommonJS behavior, where it is possible to overwrite previous exports.

[argshook]

Agree with @sramam this should be treated as a major version.

This issue, together with https://github.com/microsoft/tslib/issues/105 is painful to track down.

I also saw cases where users don’t even use typescript, but because of layers of dependencies, the issue rises up.

[DanielRosenwasser]

1.13.0 should be available for those impacted by the change. Users on TypeScript 3.9 should look into using tslib 2.0.0.