Angular: Data binding to a property existing in one of the Data Types

Question

I've just stumbled upon the following case.

Let's say we've created 2 different Interfaces, ie:

export interface bikeDetails {
  brand: string;
  wheels: number;
}

export interface carDetails {
  brand: string;
  wheels: number;
  engines: number;
}

And now in a Component.ts a Property can be of one of both Data Types:

export class MultiComponent {
 ...
 isCar: boolean;
 elementDetails: bikeDetails | carDetails;
 ...
}

When attempting to access the "engine" property of carDetails...

<div *ngIf="isCar && elementDetails">
   <h5>{{elementDetails.engines}}</h5>
</div>

...The Binding is marked in red telling me: "Identifier 'engine' is not defined. '' does not contain such a member Angular"

If I try to bind to a common property, as, ie the "brand" property, the Error is gone:

 <div *ngIf="isCar && elementDetails">
    <h5>{{elementDetails.wheels}}</h5>
 </div>

As soon as I remove the "bikeDetails" dataType from "elementDetails", the error obviously disappears.

I've tried to use the "Safe" (?) operator, but again it doesn't seem to fix it.

So, how should I bind correctly to a non-common property existing in one of the Data Types the Object could be at that particular time ?

Philip · Accepted Answer · 2019-10-28 14:05:16Z

1

You may suppress the error message by casting elementDetails to the any type in your template:

<div *ngIf="isCar && elementDetails">
   <h5>{{$any(elementDetails).engines}}</h5>
</div>

Source: https://angular.io/guide/aot-compiler#disabling-type-checking-using-any

answered Oct 28, 2019 at 14:05

Philip

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