# reject-import-system-module-from-non-system

Rejects static import declaration for system modules (`.sys.mjs`) from non-system
modules.

Using static import for a system module into a non-system module would create a separate instance of the imported object(s) that is not shared with the other system modules and would break the per-process singleton expectation.

The reason for this is that inside system modules, a static import will load the module into the shared global. Inside non-system modules, the static import will load into a different global (e.g. window). This will cause the module to be loaded into different scopes, and hence create separate instances. The fix is to use `ChromeUtils.importESModule` which will import the object via the system module shared global scope.

## Examples of incorrect code for this rule

Inside a non-system module:

```js
import { AppConstants } from "resource://gre/modules/AppConstants.sys.mjs";
```

## Examples of correct code for this rule

Inside a non-system module:

```js
const { AppConstants } = ChromeUtils.importESModule(
  "resource://gre/modules/AppConstants.sys.mjs"
);
```

Inside a system module:

```js
import { AppConstants } from "resource://gre/modules/AppConstants.sys.mjs";
```