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Detect whether the value change happened by manual or programmatic

You can check about whether value change happened by manual or programmatic by using change event argument that argument name is isInteracted.

The following example demonstrate, how to check whether value change happened by manual or programmatic.

Source
Preview
app.component.ts
app.module.ts
main.ts
index.html
import { Component , ViewChild} from '@angular/core';
import { DropDownListComponent } from '@syncfusion/ej2-angular-dropdowns';

@Component({
    selector: 'app-root',
    // specifies the template path for DropDownList component
    templateUrl: `./template.html`
})
export class AppComponent {
    constructor() {
    }
    ngAfterViewInit(){
        document.getElementById('btn').onclick = () => {
            this.dropDownListObject.value = 'game3';
        }
    }
    // defined the array of data
    public data: { [key: string]: Object }[] = [ { Id: 'game1', Game: 'Badminton' },
                 { Id: 'game2', Game: 'Football' }, { Id: 'game3', Game: 'Tennis' }];
    // maps the appropriate column to fields property
    public fields: Object = { text: 'Game', value: 'Id' };
    //set the placeholder to DropDownList input
    public text: string = "Select a game";
    @ViewChild('ddlelement')
    public dropDownListObject: DropDownListComponent;
    onChange(args): void {
        let element: HTMLElement = document.createElement('p');
        if (args.isInteracted) {
            element.innerText = 'Changes happened by Interaction';
        } else {
            element.innerText = 'Changes happened by programmatic';
        }
        document.getElementById('event').append(element);
    }
}
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule } from '@angular/forms';
import { AppComponent } from './app.component';
import { DropDownListComponent } from '@syncfusion/ej2-angular-dropdowns';
/**
 * Module
 */
@NgModule({
    imports: [
        BrowserModule,FormsModule
    ],
    declarations: [AppComponent, DropDownListComponent],
    bootstrap: [AppComponent]
})
export class AppModule { }
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { enableProdMode } from '@angular/core';
import { AppModule } from './app.module';

enableProdMode();
platformBrowserDynamic().bootstrapModule(AppModule);
<!DOCTYPE html>
<html lang="en">

<head>
    <title>Angular DropDownList</title>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta name="description" content="Typescript Toolbar Controls" />
    <meta name="author" content="Syncfusion" />
    <link href="index.css" rel="stylesheet" />
    <!-- Here we have used CDN links for our preview purpose  -->
    <link href="//cdn.syncfusion.com/ej2/ej2-dropdowns/styles/material.css" rel="stylesheet" />
    <link href="//cdn.syncfusion.com/ej2/ej2-base/styles/material.css" rel="stylesheet" />
    <link href="//cdn.syncfusion.com/ej2/ej2-popups/styles/material.css" rel="stylesheet" />
    <link href="//cdn.syncfusion.com/ej2/ej2-inputs/styles/material.css" rel="stylesheet" />
    <link href="//cdn.syncfusion.com/ej2/ej2-lists/styles/material.css" rel="stylesheet" />
    <link href="//cdn.syncfusion.com/ej2/ej2-buttons/styles/material.css" rel="stylesheet" />
    <script src="https://unpkg.com/core-js@2.6.5/client/shim.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/2.4.1/core.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/zone.js/0.6.25/zone.min.js"></script>
    <script src="https://unpkg.com/reflect-metadata@0.1.3"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/systemjs/0.19.38/system.js"></script>
    <script src="systemjs.config.js"></script>
</head>

<body>
    <div id="wrapper">
        <app-root>
            <div id='loader'>LOADING....</div>
        </app-root>
    </div>
</body>
</html>