Angular2 Observable.map capture value of local variable

Question

How can one capture value of a local variable for use inside Observable.map() callback? For example, in my Anglar2 application I would love to capture value of quantity for use in findItem().map() :

let quantity : number = 1; //<-- needs to be captured
let ordered : string[] = [];
//not interested in actual results, just adding queried items to cart
let queries : Observable<void>[] = [];
//res.entities are NLP classified entities, either item_id:string or quantity:number
for (let entity of res.entities) {
    if(entity.entity == 'item') {
        queries.push(
            this.findItem(entity.value).map(item => {
            if(item != null)
            {
                for(let i : number = quantity; i > 0; i--) this.cart.addItem(item);
            }
            ordered.push(quantity + 'x ' + item.fullName);//NL message for user
        }));
        quantity = 1;//reset quantity
    }
    else if(entity.entity == 'quantity') quantity = entity.value;
}
return Observable.forkJoin(queries, ...);

The ordered will show quantity 1 for all items (because value of quantity is always 1 at the end of the loop).
My research shows that this is very common problem in JavaScript, and there are plenty of examples how to capture a variable in for loops. I wasn't able, however, to find any information how to capture variable values for use in callback s, such as Observable.map()

Answer 1

Use a const within your for loop.

for (let entity of res.entities) {
    if(entity.entity == 'item') {
        const q = quantity; //here or somewhere
        queries.push(
            //..... use q instead
    }
    else if(entity.entity == 'quantity') quantity = entity.value;
}