Fire an event when window is scrolled to a particular section of the page, using jQuery

Question

I am trying to fire an event when the window is scrolled to a particular section of the page, using jQuery. I have checked some of the previous posts on Stack Overflow, itself, but am not able to find any solution.

$(document).ready(function() {

  $(".navbar-links").click(function() {
    $(".navbar-links").removeClass("active");
    $(this).addClass("active");
  });

  var portfolio_offset = $("#portfolio-section").offset().top();

  $(window).scroll(function() {
    alert("Hi !");
    var scrolled_offset = window.pageYOffset;
    if (scrolled_offset >= portfolio_offset) {
      alert("hi");
      $(".navbar-links").removeClass("active");
      $("#portfolio-section").addClass("active");
    }
  });

  $("#fb_btn").click(function() {
    alert("hi");
    document.location = "https://www.facebook.com/rishabh.kashyap.940436";
  });

});

button {
  background: transparent;
  border: 1px solid white;
}

#about-section {
  background-color: #fd746c;
  color: black;
}

#portfolio-section {
  background-color: #904e95;
  color: black;
}

#contact-section {
  background-color: #4ca1af;
  color: black;
}

.active {
  border: 1px solid white;
}

#navbar-menu {
  text-align: center;
}

.heading {
  font-family: Sofia;
}

.navbar {
  background-color: black;
}

.content {
  font-family: Lily Script One;
}

.navbar-brand {
  font-size: 27px;
}

.content-div {
  text-align: center;
  display: inline-block;
  vertical-align: middle;
  float: none;
}

.navbar-links {
  font-size: 20px;
}

.center {
  text-align: center;
}

img {
  border: 1px solid white;
  margin: auto;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
}

.project-img {
  max-width: 70%;
  max-height: 70%;
}

.fa {
  padding: 20px;
  font-size: 45px;
  width: 100px;
  text-align: center;
  text-decoration: none;
  margin: 10px 10px;
  background: #2c4762;
  color: white;
}

.fa:hover {
  opacity: 0.7;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<nav class="navbar navbar-inverse navbar-fixed-top">
  <div class="container-fluid">
    <div class="row" id="navbar-section">
      <div class="col-md-offset-1 col-md-10 col-sm-offset-1 col-sm-10">
        <div class="navbar-header heading">
          <button class="navbar-toggle" data-toggle="collapse" data-target="#navbar-menu"><span class="glyphicon glyphicon-triangle-bottom"></span></button>
          <a href="#" class="navbar-brand">Portfolio Page</a>
        </div>
        <div id="navbar-menu" class="collapse navbar-collapse">
          <ul class="nav navbar-nav navbar-right heading">
            <li class="navbar-links active"><a href="#about-section">About</a>
              <li>
                <li class="navbar-links"><a href="#portfolio-section">Portfolio</a>
                  <li>
                    <li class="navbar-links"><a href="#contact-section">Contact</a>
                      <li>
          </ul>
        </div>
      </div>
    </div>
  </div>
</nav>
<div class="container-fluid" id="scrollable-div">
  <div class="row" id="about-section">
    <br>
    <br>
    <div class="center heading">
      <h1>About</h1>
    </div>
    <div class="col-md-offset-1 col-md-10 col-sm-offset-1 col-sm-10 col-xs-offset-1 col-xs-10">
      <div class="row">
        <div class="col-md-offset-1 col-md-6 col-sm-offset-1 col-sm-6 col-xs-offset-1 col-xs-10 content-div content">
          <h3>Rishabh Kashyap</h3>
          <h3>Full Stack Web Developer</h3>
          <h3>Key Interests - JavaScript & MEAN Stack</h3>
          <h3>Worked as an intern @ Sapient Global Markets</h3>
          <h4><i>"Never be afraid to take risks. If you succeed, you can lead and if you fail, you can guide."</i>
            <h4>
              <h4>- Swami Vivekananda</h4>
              <h3>Indeed. The motto, I try to live by. Professionally, as well as, Personally.</h3>
        </div>
        <div class="col-md-4 col-sm-4 col-xs-12 content-div">
          <img class="img-responsive project-img" alt="my image" src="https://lh3.googleusercontent.com/34CJNU0DexpintEhsM5-zcZdT_7mRWVA6dE-7f122WM3xj4xFI0nXYQhXyEG8tyrd4piHPHPGtCNtu_o5vqZ2eFFH2W9YS4ekKCqw7wgZzAjsKD8hdNoV5DrARz7I-BRljjksmdfHxoHaGIgwxcNYRJkEBa2FLIhbluVGZo1qN3zZ1ZJ1WpRU27mBbrCScNzazuOFtY0lOBX4JAKd7yGlC7ILwg4gAy-KsN-ZJz54PoNeCblgrz3jGsF8YvEf5Hc-V3kV8DtrDiKiwTpXPowvrLdldS-rIlOpjq1LrbPVNxWUNB1YieiqOUo1AEVYaS9WxiIFae2etL7Jb4nAW9MkLHE-YvQZ4VVcntRfXS3CBnuoy6EPHu2vfevnNeK9lgANs4rb1MNyMCxOACWmn45_vZKZoPfnmk_cyVzt7m2vFZUXPMdyeSRrViQD9VteriL89XHZlItrlgIhXI1vt5JAASHdOYrNV3CTpWMGPfzQk0BfQbbr2qcxnbgbSyEmK4M1wIloFQ0O_q-MCOdffySKCmct8iHRRrAcG5cWF_ArcX5GptL3tHAQHu9UCyfrjwIyI28NbrgZM0NkxxmpRAV5nRJGQetgxewxGaS2A6xfWnlW8jP-P4z=w479-h638-no?.jpg"
          />
        </div>
      </div>
    </div>
  </div>
  <div class="row" id="portfolio-section">
    <br>
    <br>
    <div class="center heading">
      <h1>Portfolio</h1>
    </div>
    <div class="col-md-offset-1 col-md-10 col-sm-offset-1 col-sm-10 col-xs-offset-1 col-xs-10">
      <img class="img-responsive project-img" alt="portfolio page" src="http://www.thefamouspeople.com/profiles/images/swami-vivekananda-3.jpg" />
      <h4><i>A tribute page to Swami Vivekananda using basic HTML & Bootstrap.</i></h4>
    </div>
  </div>
  <div class="row" id="contact-section">
    <br>
    <br>
    <div class="center heading">
      <h1>Contact Me</h1>
    </div>
    <div class="col-md-offset-1 col-md-10 col-sm-offset-1 col-sm-10 col-xs-offset-1 col-xs-10">
      <div class="center content">
        <h4><i>rishabhkashyap.rk@gmail.com</i></h4>
      </div>
      <br>
      <div class="center">
        <button class="fa fa-facebook" id="fb_btn"></button>
        <button class="fa fa-twitter" href="https://twitter.com/iamrkcheers" id="twitter_btn"></button>
        <button class="fa fa-github" href="https://github.com/iamrkcheers" id="github_btn"></button>
        <button class="fa fa-free-code-camp" href="https://www.freecodecamp.com/iamrkcheers" id="fcc_btn"></button>
        <button class="fa fa-linkedin" href="https://www.linkedin.com/in/rishabh-kashyap-735879117/" id="linkedin_btn"></button>
      </div>
    </div>
  </div>
  <div class="row" id="meta-section">
    <div class="col-md-offset-1 col-md-10 col-sm-offset-1 col-sm-10 col-xs-offset-1 col-xs-10">
    </div>
  </div>
</div>