How can I check that multiple async operations have completed?

I have a case where I want to do something once 10 async calls have completed

let i = 0;
let array = [];

do {
  this.service.getSomething(i).subscribe(response => {
    array[i] = response;
  });
} while (i < 10);

// how can I know when the 10 async calls have completed?

How can I achieve this?