Angular 7 behavior subject with class object

Question

I have below class

export class filter {
    public PageRecords: number;
    public SearchText: string;
    public SortColumn: string = null;
    public SortDirection: string = null;
    public StartingPos: number;
}

Below behavior subject

filterParam = new BehaviorSubject(new filter);

Updating subject

this.filterParam.next(<filter>{StartingPos  : 1,PageRecords : 10 })

When I get the value of subject

this.filterParam.value

It only have two props StartingPos and PageRecords which I updated. it lost other props.

How to resolve this?

Answer 1

It is because you don't pass directly a Filter object class. You are casting some dynamic json to a filter object but only with this two properties.

You can do something like this:

const filterParam = new filter();
filterParam.StartingPos = 1;
filterParam.PageRecords = 10;

this.filterParam.next(filterParam);

EDIT: I didn't notice that you want just update two values from the BehaviorSubject value. As @ritaj suggested in a comment below this aswer you can do something like he suggested:

this.filterParam.next(Object.assign(this.filterParam.value, {StartingPos: 1, PageRecords: 10 }

Object.assign() copies the values (of all enumerable own properties) from one or more source objects to a target object. It has a signature of Object.assign(target, ...sources). The target object is the first parameter and is also used as the return value. Object.assign() is useful for merging objects or cloning them shallowly.