onchange su seleziona tag
<select id="comboA" onchange="getComboA(this)">
<option value="">Select combo</option>
<option value="Value1">Text1</option>
<option value="Value2">Text2</option>
<option value="Value3">Text3</option>
</select>
evento onchange
<select class='select-option' [(ngModel)]="selected"
(change)='onOptionsSelected($event)'>
<option class='option' *ngFor='let option of dropDownData'
[value]="option.seo_val">{{option.text_val}}</option>
</select>
public onOptionsSelected(event) {
const value = event.target.value;
this.selected = value;
console.log(value);
}