Chaining http calls in angular 2 in a for loop

I have some code that looks like

//service.ts

addProduct(productId) {
   this.http.post('someUrl', ReqData).map(json).subscribe(doStuff);
}

//component.ts

addAllproducts(productsIds) {
   productIds.forEach(productId => service.addProduct(productId);
}

What I want is to be able to wait for each call to finish before calling for the next productId, without using window.setTimeout ..