Using parameters as part of an object property chain

Question

In Angular, I have interfaces which look like this (this is not my code):

export interface Vehicles {
    id: number;
    cars: Car;
    trucks: Truck;
}

Export interface Car {
    make: number;
    model: number;
}

Export interface Truck {
    make: number;
    model: number;
}

My service contains two functions doCarMath() and doTruckMath() that do calculations based on the API's returned values:

vehicleNumbers: Vehicles;

constructor(private http: HttpClient) {
    this.vehicleNumbers = {};
}

callID(id: string): Observable<Vehicles>{
    return this.http.get<Vehicles>(this.myURL+`/${id}`);
}

getMyCarNumbers(id) {
    this.callID(id).subscribe(results =>
    {
        this.vehicleNumbers = results;
    }
}

doCarMath(): number {
    return this.vehicleNumbers.car.make; / this.vehicleNumbers.car.model;
}

doTruckMath(): number {
    return this.vehicleNumbers.truck.make; / this.vehicleNumbers.truck.model;
}

I’d like to combine doCarMath() and doTruckMath() into one doMath() function by passing in an argument to specify either car or truck, like so:

doMath(p_vehicle): number {
    return this.vehicleNumbers.p_vehicle.make/this.vehicleNumbers.p_vehicle.model; // can p_vehicle be used here?
}

How can I use parameter p_vehicle here? The above throws intellisense errors for the p_vehicle parameter, but I don't have the code locally and can't share the error.

Do you mean Dynamically access object property using variable? — VLAZ
– VLAZ, Commented Jan 5, 2021 at 9:39
Also, for what it's worth, using OOP and polymorphism here would vastly simplify your code. — VLAZ
– VLAZ, Commented Jan 5, 2021 at 9:45

SeleM · Accepted Answer · 2021-01-05 09:40:22Z

2

I think this would do the job:

doMath(p_vehicle): number {
    return this.vehicleNumbers[p_vehicle].make/this.vehicleNumbers[p_vehicle].model; 
}

Then calling the function would be :

doMath('car'); // or this.doMath('car');
doMath('truck'); // or this.doMath('truck');

answered Jan 5, 2021 at 9:40

SeleM

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2 Comments

Kyle Vassella Over a year ago

Thank you! Can you stack bracket notation more than once? Originally the properties looked like return this.vehicleNumbers.car.carMake; / this.vehicleNumbers.car.carModel;. Can I also pass in parameters [p_vehicleMake] and [p_vehicleModel] to access carMake and carModel like so:

doMath(p_vehicle, p_vehicleMake, p_vehicleModel): number {     return this.vehicleNumbers[p_vehicle].[p_vehicleMake]/this.vehicleNumbers[p_vehicle].[p_vehicleModel]; }

?

SeleM Over a year ago

yes you can but be careful: NO '.' (points) between brackets ([a][b] >> is >> a.b)

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