data-toggle not working in any browser

Here is my code. data-toggle is not working for navigation bar

I should be able to see navbar when I minimize the browser window. This is my code:

<meta name="viewport" content="width=device-width, initial-scale=1" />

<nav class="navbar navbar-inverse navbar-fixed-top">
    <div class="container-fluid">
        <div class="navbar-header">
            <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-expanded="false" aria-controls="navbar">
                <span class="sr-only">Toggle navigation</span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
            </button>
            <a class="navbar-brand" href="home.html">Form Maker</a>
        </div>
        <div id="navbar" class="navbar-collapse collapse">
            <ul class="nav navbar-nav navbar-right">
                <li><a href="./register.html">Register</a></li>
                <li><a href="./login.html">Login</a></li>
                <li><a href="#">Username</a></li>
                <li><a href="#">Logout</a></li>
            </ul>
        </div>
    </div>
</nav>