Angular2 select-option dropdown dynamic loading on HTML page load

Question

I have a HTML page where I am using 2 select - option drop-down I want to fill the second drop-down on the basis of what is selected in the first drop-down.

Actually there are 2 drop-downs I have some values in first drop-down on-loading the page for first time one is selected depending on API result, now I want to bind the list to second drop-down based on what is selected in first drop-down.

Can anyone help me in doing that in Angular 2 HTML select-option

<td>
    <div>
        <select #selectedHeading (change)="headingChanged($event.target.selectedIndex)" [disabled]='butDisabled'>
            <option *ngFor="let heading of headings" [value]="heading.val" [ngValue]="accountitem" [selected]="accountitem.heading === heading.val" >
               {{heading.val}}
            </option>
        </select>
    </div>
</td>
<td>{{accountitem.rules}}</td>
<td>
    <select #selectedSubHeading [disabled]='butDisabled'>
        <option *ngFor="let subHeading of subHeadings" [value]="subHeading.val">{{subHeading.val}}</option>
    </select>
</td>

Answer 1

change this variable to count++ in ngOnInit() and we will check in inside this method.

count:number=0;
    headingChanged(receivePraam){
    if(count){
this.butDisabled=true;
    }
    else{
this.butDisabled=false;
}
    //and here set dropdown2 value.
    }