wijmo.angular2.grid.sheet is an external TypeScript module that can be imported to your code using its ambient module name. For example:

import * as wjSheet from 'wijmo/wijmo.angular2.grid.sheet';
 
@Component({
    directives: [wjSheet.WjFlexSheet],
    template: `<wj-flex-sheet></wj-flex-sheet>`,
    selector: 'my-cmp',
})
export class MyCmp {
}