@types/systemjs

const System: {
    import: System.ImportFn;
    register(dependencies: string[], declare: System.DeclareFn): void;
    register(name: string, dependencies: string[], declare: System.DeclareFn): void;
    resolve(moduleId: string, parentUrl?: string): string;
    delete(moduleId: string): false | System.UpdateModuleFn;
    get(moduleId: string): System.Module | null;
    get<T>(moduleId: string): T;
    has(moduleId: string): boolean;
    set(moduleId: string, module: System.Module): void;
    entries(): Iterable<[string, System.Module]>;
    addImportMap(importMap: System.ImportMap): void;
};