Angular 4 - Select default value in dropdown [Reactive Forms]

I was struggling and Found this Easy and Effective way from IntelliJ IDEA suggestion

<select id="country" formControlName="country"  >
  <option [defaultSelected]=true [value]="default" >{{default}}</option>
  <option *ngFor="let c of countries" [value]="c" >{{ c }}</option>
</select> 

And On your ts file assign the values

 countries = ['USA', 'UK', 'Canada'];
 default = 'UK'

Just make sure your formControlName accepts string, because you already assigned it as a string.

Try like this :

component.html

<form [formGroup]="countryForm">
    <select id="country" formControlName="country">
        <option *ngFor="let c of countries" [ngValue]="c">{{ c }}</option>
    </select>
</form>

component.ts

import { FormControl, FormGroup, Validators } from '@angular/forms';

export class Component {

    countries: string[] = ['USA', 'UK', 'Canada'];
    default: string = 'UK';

    countryForm: FormGroup;

    constructor() {
        this.countryForm = new FormGroup({
            country: new FormControl(null);
        });
        this.countryForm.controls['country'].setValue(this.default, {onlySelf: true});
    }
}

In Reactive forms. Binding can be done in the component file and usage of ngValue. For more details please go through the following link

https://angular.io/api/forms/SelectControlValueAccessor

import {Component} from '@angular/core';
import {FormControl, FormGroup} from '@angular/forms';

@Component({
  selector: 'example-app',
  template: `
    <form [formGroup]="form">
      <select formControlName="state">
        <option *ngFor="let state of states" [ngValue]="state">
          {{ state.abbrev }}
        </option>
      </select>
    </form>

       <p>Form value: {{ form.value | json }}</p> 
       <!-- {state: {name: 'New York', abbrev: 'NY'} } -->
    `,
})
export class ReactiveSelectComp {
  states = [
    {name: 'Arizona', abbrev: 'AZ'},
    {name: 'California', abbrev: 'CA'},
    {name: 'Colorado', abbrev: 'CO'},
    {name: 'New York', abbrev: 'NY'},
    {name: 'Pennsylvania', abbrev: 'PA'},
  ];

  form = new FormGroup({
    state: new FormControl(this.states[3]),
  });
}