Set default option in mat-select

Solution 1:

Working StackBlitz

No need to use ngModel or Forms

In your html:

 <mat-form-field>
  <mat-select [(value)]="selected" placeholder="Mode">
    <mat-option value="domain">Domain</mat-option>
    <mat-option value="exact">Exact</mat-option>
  </mat-select>
</mat-form-field>

and in your component just set your public property selected to the default:

selected = 'domain';

Solution 2:

Try this

<mat-form-field>
    <mat-select [(ngModel)]="modeselect" [placeholder]="modeselect">
        <mat-option value="domain">Domain</mat-option>
        <mat-option value="exact">Exact</mat-option>
    </mat-select>
</mat-form-field>

Component:

export class SelectValueBindingExample {
    public modeselect = 'Domain';
}

Live demo

Also, don't forget to import FormsModule in your app.module