Toggle button not working in bootstrap 4 and angular 7 app for navbar

I am working with Angular7 and Botstrap4. trying to add navbar in my app, when navbar is collapsed, toggle button not working.

I don't want to add ng-bootstrap, only bootstrap4.

Here is my code

<nav class="navbar navbar-expand-lg navbar-light bg-light">
  <a class="navbar-brand" href="#">{{title}}</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarTogglerDemo02" aria-controls="navbarTogglerDemo02" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>

  <div class="collapse navbar-collapse" id="navbarTogglerDemo02">
    <ul class="navbar-nav mr-auto mt-2 mt-lg-0">
      <li class="nav-item active">
        <a class="nav-link" routerLink="home">Home <span class="sr-only">(current)</span></a>
      </li>
      <li class="nav-item">
        <a class="nav-link" routerLink="about">About Us</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" routerLink="contact">Contact Us</a>
      </li>
    </ul>

    <form class="form-inline my-2 my-lg-0">
      <input class="form-control mr-sm-2" type="search" placeholder="Search">
      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
    </form>
  </div>
</nav>