With my angular2 application, i am getting the response and assigning to object as follows,

 seatingConcession: {
                        parking: data.concession.extras.parking ? data.concession.extras.parking : null,
                        restrictedview: data.concession.extras.restrictedview ? data.concession.extras.restrictedview : null,
                        wheelchair: data.concession.extras.wheelchair ? data.concession.extras.wheelchair : null
                    }

sometimes extras does not have value. sometimes restrictedview inside extras does not have value. what is the best way to check and assign the default value . Whole code:

 this.eventService.getListingsByEventId(this.eventId).subscribe(listresults => {
            this.bindListing(listresults);
        }, error => this.errorMessage = error);
    }
    bindListing(listres: any[]) {
        let price_table = {};
        let section_table = {};
        listres.forEach((data) => {
            data.ticket.seating.forEach((seat: any) => {
                // tslint:disable-next-line:max-line-length
                this.listings.push({
                    section: seat.section, selling: data.price.selling, amount: data.ticket.amount, type: data.ticket.type, row: seat.row, category: seat.category,
                    seatingConcession: {
                        parking: data.concession.extras ? (data.concession.extras.restrictedview || null) : null,
                        restrictedview: data.concession.extras.restrictedview || null,
                        wheelchair: data.concession.extras.wheelchair  || null
                    },
                    deliveryconcession: {
                        instantdownload: data.delivery.instantdownload || null,
                        readytoship: data.delivery.readytoship  || null,
                        unespecifiedshipment: data.delivery.unspecifiedshipment  || null
                    }
                });
                // this.listings.push({ section: seat.section, selling: data.price.selling, amount: data.ticket.amount, type: data.ticket.type, row: seat.row, category: seat.category});
                // tslint:disable-next-line:curly
                if (!price_table.hasOwnProperty(data.price.selling))
                    price_table[data.price.selling] = [];
                price_table[data.price.selling].push(data);
                // tslint:disable-next-line:curly
                if (!section_table.hasOwnProperty(seat.section))
                    section_table[seat.section] = [];
                section_table[seat.section].push(data);
            });
        });

Service js:

 getListingsByEventId(EventID: string): Observable<ListingSeller[]> {
        let apiurl = this.appConfig.getAPIUrl() + '/getListingsByEventId';

        return this.http
            .get(apiurl + queryString)
            .map(this.extractData)
            .catch(this.handleErrors);
    }

You can use the following function to achieve what you want.

function getSafe(fn) {
    try {
        return fn();
    } catch (e) {
        return null;
    }
}

Then use it like this

seatingConcession: {
    parking: getSafe(() => data.concession.extras.parking),
    restrictedview: getSafe(() => data.concession.extras.restrictedview),
    wheelchair: getSafe(() => data.concession.extras.wheelchair),
}

See details.

Another approach would be to execute data.concession.extras = data.concession.extras || {} before actually creating your object.

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