primeng <p-dropdown> get previous selected value

Question

I want to get the previous selected value in primeng dropdown .

<p-dropdown [options]="options" [filter]="true" [(ngModel)]="selectedType" (onChange)="onSelectType($event)" formControlName="alertType"></p-dropdown>

On change event I want to check whether the selected type is valid using an api, but need to revert if it is invalid. Since I am using ngModel, the value of selectedType is changing whenever the dropdown value changes.

So how can I get the previous selected value?

Answer 1

This sample example of ngModelChange :

app.component.html

<p-dropdown [options]="cities" [(ngModel)]="selectedCity" (ngModelChange)="onSelectType($event)"></p-dropdown>

app.component.ts

import { SelectItem } from 'primeng/primeng';

export class AppComponent {
    cities: SelectItem[];
    selectedCity: any;
    previousVal: any;
    currentVal: any;

    constructor() {
        this.cities = [{
            "label": "London",
            "value": "london"
        }, {
            "label": "USA",
            "value": "usa"
        }];
    }

   onSelectType(event) {
       if(event) {
           this.previousVal = this.currentVal;
           this.currentVal = event;
       }
       console.log('this.previousVal', this.previousVal);
       console.log('this.currentVal', this.currentVal);
   }
}

app.module.ts

import { DropdownModule } from 'primeng/primeng';

imports: [ DropdownModule ]

solution is use ngModelChange ;