title: Toggle button not working in bootstrap 4 and angular 7 app for navbar
body: <p>I am working with Angular7 and Botstrap4.
  trying to add navbar in my app, when navbar is collapsed, toggle button not working.</p>
  
  <p>I don't want to add ng-bootstrap, only bootstrap4.</p>
  
  <p>Here is my code</p>
  
  <pre><code>&lt;nav class="navbar navbar-expand-lg navbar-light bg-light"&gt;
    &lt;a class="navbar-brand" href="#"&gt;{{title}}&lt;/a&gt;
    &lt;button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarTogglerDemo02" aria-controls="navbarTogglerDemo02" aria-expanded="false" aria-label="Toggle navigation"&gt;
      &lt;span class="navbar-toggler-icon"&gt;&lt;/span&gt;
    &lt;/button&gt;
  
    &lt;div class="collapse navbar-collapse" id="navbarTogglerDemo02"&gt;
      &lt;ul class="navbar-nav mr-auto mt-2 mt-lg-0"&gt;
        &lt;li class="nav-item active"&gt;
          &lt;a class="nav-link" routerLink="home"&gt;Home &lt;span class="sr-only"&gt;(current)&lt;/span&gt;&lt;/a&gt;
        &lt;/li&gt;
        &lt;li class="nav-item"&gt;
          &lt;a class="nav-link" routerLink="about"&gt;About Us&lt;/a&gt;
        &lt;/li&gt;
        &lt;li class="nav-item"&gt;
          &lt;a class="nav-link" routerLink="contact"&gt;Contact Us&lt;/a&gt;
        &lt;/li&gt;
      &lt;/ul&gt;
  
      &lt;form class="form-inline my-2 my-lg-0"&gt;
        &lt;input class="form-control mr-sm-2" type="search" placeholder="Search"&gt;
        &lt;button class="btn btn-outline-success my-2 my-sm-0" type="submit"&gt;Search&lt;/button&gt;
      &lt;/form&gt;
    &lt;/div&gt;
  &lt;/nav&gt;
  </code></pre>