Call a global variable inside module

You need to tell the compiler it has been declared:

declare var bootbox: any;

If you have better type information you can add that too, in place of any.

For those who didn't know already, you would have to put the declare statement outside your class just like this:

declare var Chart: any;

@Component({
  selector: 'my-component',
  templateUrl: './my-component.component.html',
  styleUrls: ['./my-component.component.scss']
})

export class MyComponent {
    //you can use Chart now and compiler wont complain
    private color = Chart.color;
}

In TypeScript the declare keyword is used where you want to define a variable that may not have originated from a TypeScript file.

It is like you tell the compiler that, I know this variable will have a value at runtime, so don't throw a compilation error.