Bootstrap 4: Dropdown menu is going off to the right of the screen

Question

Bootstrap has this built in already: See Menu Alignment. Just add the dropdown-menu-right class to the dropdown-menu div.

<div class="dropdown-menu dropdown-menu-right">

Working Example: (open Full Page)

<link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.5.0/css/bootstrap.min.css" rel="stylesheet" />
<nav class="navbar navbar-expand-xl navbar-dark bg-primary">

  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
    </button>

  <a class="navbar-brand" href="#">Company</a>

  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <form action="#" class="form-inline my-2 my-lg-0">
      <input class="form-control mr-sm-2" id="keyword" name="keyword" :value='keyword' type="text" placeholder="Search for jobs" />
      <input class="form-control mr-sm-2" id="location" name="location" :value='location' type="text" placeholder="Location" />
      <button class="btn btn-secondary my-2 my-sm-0" type="submit">Find Jobs</button>
    </form>

    <ul class="navbar-nav mr-auto">
      <li class="nav-item">
        <a href="#" class="nav-link active">
          <strong>Post Job</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>Register</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>Profile</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>My Jobs</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>My Searches</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>Employer Dashboard</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>Login</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>Logout</strong>
        </a>
      </li>
    </ul>

    <ul class="navbar-nav">
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          <strong>Account</strong>
        </a>
        <div class="dropdown-menu dropdown-menu-right" aria-labelledby="navbarDropdown">
          <a class="dropdown-item">
            <strong>Register</strong>
          </a>
          <a href="#" class="dropdown-item">
            <strong>Profile</strong>
          </a>
          <a href="#" class="dropdown-item">
            <strong>My Jobs</strong>
          </a>
          <a href="#" class="dropdown-item">
            <strong>My Searches</strong>
          </a>
          <a href="#" class="dropdown-item">
            <strong>Employer Dashboard</strong>
          </a>
          <a href="#" class="dropdown-item">
            <strong>Login</strong>
          </a>
          <a href="#" class="dropdown-item">
            <div class="dropdown-divider"></div>
            <strong>Logout</strong>
          </a>
        </div>
      </li>
    </ul>
  </div>
</nav>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/2.4.2/umd/popper.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.5.0/js/bootstrap.min.js"></script>

For the benefit of those who stumble upon this issue when googling but are using react, the accepted answer (whilst correct) won't solve the issue for you. React ignores 'dropdown-menu-right' when you add it manually to the className. Instead, update your code to the below and it correctly sets the same class.

For javascript

<DropdownMenu right>

For typescript

<DropdownMenu right={true}>

Putting it in here as this thread appeared when I was googling the issue and took me quite a while to figure out the correct solution for bootstrap 4 in react (reactstrap).

In your style sheet, for .dropdown-menu change left: 0; to right: 0;.

In Bootstrap 5 (beta 2) you can use dropdown-menu-end:

<div class="dropdown-menu dropdown-menu-end">
  ...
</div>

I was looking over your code and I think the accepted answer addresses a different problem. If the menu move to the left or the right of the page and is not under the button, it is because you are missing the parent class .btn-group and it seems like your .dropdown-toggle and .dropdown-menu classes are on the wrong elements. Here is the most basic example from the Bootstrap 4 docs.

<div class="btn-group">
  <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    Right-aligned menu
  </button>
  <div class="dropdown-menu dropdown-menu-right">
    <button class="dropdown-item" type="button">Action</button>
    <button class="dropdown-item" type="button">Another action</button>
    <button class="dropdown-item" type="button">Something else here</button>
  </div>
</div>

I only went over a small block of your code, but at the end where you have a dropdown on large screens, I focused on this.

 <li class="nav-item dropdown"> <!--- change this line --->
            <a class="nav-link dropdown-toggle" href="/" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
              <strong>Account</strong>
            </a>
            <div class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">

              <!-- <li v-if="!user_logged" class="nav-item"> -->
              <a v-if="!user_logged" href="/signup" class="dropdown-item"><strong>Register</strong></a>
              <!-- </li> -->

              <!-- <li v-if="user_logged && user_type === 'user'" class="nav-item"> -->
              <a v-if="user_logged && user_type === 'user'" href="/profile" class="dropdown-item"><strong>Profile</strong></a>
              <a v-if="user_logged && user_type === 'user'" href="/applied" class="dropdown-item"><strong>My Jobs</strong></a>
              <a v-if="user_logged && user_type === 'user'" href="/searches" class="dropdown-item"><strong>My Searches</strong></a>

              <!-- </li> -->

              <!-- <li v-if="user_logged && user_type === 'company'" class="nav-item"> -->
              <a v-if="user_logged && user_type === 'company'" href="/dashboard" class="dropdown-item"><strong>Employer Dashboard</strong></a>
              <!-- </li> -->

              <!-- <li v-if="!user_logged" class="nav-item"> -->
              <a v-if="!user_logged" href="/login" class="dropdown-item"><strong>Login</strong></a>
              <!-- </li> -->

              <!-- <li v-if="user_logged" class="nav-item"> -->
              <a v-if="user_logged" href="/logout" class="dropdown-item">
                <div class="dropdown-divider"></div>
                <strong>Logout</strong>
              </a>
              <!-- </li> -->
            </div>

          </li>

to

 <li class="nav-item btn-group">
            <a class="nav-link dropdown-toggle" href="/" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
              <strong>Account</strong>
            </a>
            <div class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">

              <!-- <li v-if="!user_logged" class="nav-item"> -->
              <a v-if="!user_logged" href="/signup" class="dropdown-item"><strong>Register</strong></a>
              <!-- </li> -->

              <!-- <li v-if="user_logged && user_type === 'user'" class="nav-item"> -->
              <a v-if="user_logged && user_type === 'user'" href="/profile" class="dropdown-item"><strong>Profile</strong></a>
              <a v-if="user_logged && user_type === 'user'" href="/applied" class="dropdown-item"><strong>My Jobs</strong></a>
              <a v-if="user_logged && user_type === 'user'" href="/searches" class="dropdown-item"><strong>My Searches</strong></a>

              <!-- </li> -->

              <!-- <li v-if="user_logged && user_type === 'company'" class="nav-item"> -->
              <a v-if="user_logged && user_type === 'company'" href="/dashboard" class="dropdown-item"><strong>Employer Dashboard</strong></a>
              <!-- </li> -->

              <!-- <li v-if="!user_logged" class="nav-item"> -->
              <a v-if="!user_logged" href="/login" class="dropdown-item"><strong>Login</strong></a>
              <!-- </li> -->

              <!-- <li v-if="user_logged" class="nav-item"> -->
              <a v-if="user_logged" href="/logout" class="dropdown-item">
                <div class="dropdown-divider"></div>
                <strong>Logout</strong>
              </a>
              <!-- </li> -->
            </div>

          </li>