How to get Length from Array Model in Typescript

Question

I am trying to get the length from Array interface. But getting error as:

error TS2339: Property 'length' does not exist on type 'ModelSubSystems'. In this case how to get the length. here is my TS code:

@Input() subsystems: ModelSubSystems;

resolve({ data: this.subsystems, totalCount: this.subsystems.length }); //error

here is my interfaces:

export interface ModelSubSystem {
    Id: number;
    Name: string;
    CreatedBy: string;
    CreatedDate: Date;
    UpdatedBy: string;
    UpdatedDate: Date;
}

export interface ModelSubSystems {
    subsystems: Array<ModelSubSystem>; //this is array!!
}

any one help me with correct approach. Thanks in advance.

Do you want this.subsystems.length, or this.subsystems.subsystems.length? — Jeff Bowman
– Jeff Bowman, Commented Jun 17, 2019 at 5:19
@JeffBowman - I tried with declaring @Input() subsystems: ModelSubSystems.subsystem; but got the error as @Input() subsystems: ModelSubSystems.subsystem; But getting warning as ModelSubSystems only refer to a type, but being used as a name space here — user2024080
– user2024080, Commented Jun 17, 2019 at 5:35

Nabil Shahid · Accepted Answer · 2019-06-17 05:42:41Z

3

@Input() subsystems: ModelSubSystems this input variable will not have length because it is an interface with one property whose name is subsystems as well and is an array(the one you are trying to get length of).

The array property created in the interface can be accessed using this.subsystems.subsystems while the first subsystem here is you input of type systemsystem and the second one is the array in that interface.

If you want the subsystems input to be to be an array of ModelSubSystem, instead of creating ModelSubSystems interface, directly declare this input as and array so that you can access its length:

@Input() subsystems: Array<ModelSubSystem>

edited Jun 17, 2019 at 5:42

answered Jun 17, 2019 at 5:26

Nabil Shahid

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2 Comments

user2024080 Over a year ago

I declared like this: @Input() subsystems: ModelSubSystems.subsystem; But getting warning as ModelSubSystems only refer to a type, but being used as a name space here

user2024080 Over a year ago

But sad to see why my ModelSubSystems not helped here.

Titulum · Accepted Answer · 2019-06-17 05:30:46Z

1

Are you certain that the this.subsystems variable is initialised instead of only declared?

Typescript interface variables are undefined by default, so you will have to set them before they can be used / their methods can be called.

EDIT: as Jeff Bowman pointed out, what you actually need is this.subsystems.subsystems.length.

You could also add the length property to the interface, and have a class implement the desired behavior:

export interface IModelSubSystems {
  subsystems : Array<ModelSubSystem>;
  length : number;
}

export class ModelSubSystems implements IModelSubSystems {
  subsystems = new Array<ModelSubSystem>();
  get length() : number {
    return this.subsystems.length;
  }
}

edited Jun 17, 2019 at 5:30

answered Jun 17, 2019 at 5:22

Titulum

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