Extracting a field from an array of objects in Angular is a powerful feature

I'm feeling a bit confused and would appreciate some explanations please!

In my code, I have a datatable that generates an array of Operation objects in my .ts file. Here is the object class:

export class Operation {
  id: number;
  name: string;
}

This is how the array is declared:

selectedOperations: Operation[]; 

When I log the selected operations in the console before extracting ids, I see this:

this.selectedOperations = {"selected":[{"id":1,"name":"My name 1"},{"id":3,"name":"My name 3"}]}

But when I try to extract ids using this code snippet:

let ids = this.selectedOperations.map(o => o.id);

I encounter an exception:

this.selectedOperations.map is not a function

I've faced similar issues before and I'm trying to understand why. Could it be related to differences between Array and object[]? The presence of {"selected": before the array makes me doubt if it's truly an array...

If anyone could shed some light on this issue and help me extract the ids, I would greatly appreciate it!

Thank you so much!

Answer №1

{"selected":[{"id":1,"name":"My name 1"},{"id":3,"name":"My name 3"}]} is an object, while your array declaration for selectedOperations seems incorrect: Operation[];

You can either assign the array directly to your variable:

this.selectedOperations = [{"id":1,"name":"My name 1"},{"id":3,"name":"My name 3"}];

Alternatively, you can change the variable type to any or object:

selectedOperations: any;

this.selectedOperations = {"selected":[{"id":1,"name":"My name 1"},{"id":3,"name":"My name 3"}]}

const ids = this.selectedOperations.selected.map(o => o.id);

The error "this.selectedOperations.map is not a function" occurs because the initialization is done on an object. The map function is only available for arrays, hence the error when using it with an object type variable.

It's better to follow the first approach as declaring a variable as any or object goes against the purpose of TypeScript.

Answer №2

To enhance the code, you must make some adjustments. To retrieve the ids, include selected in this.selectedOperations. Look at the example below.

let ids = this.selectedOperations.selected.map(o => o.id);

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