Switch Bootstrap 4 hamburger menu with Vanilla JS

Introduction

Some weeks ago, I wrote a small ASP.NET MVC application where I already have to Search and filter a table with JavaScript.

This application uses Bootstrap 4, which allows me to have a totally responsive result without too much effort. In particular the navigation bar is fully displayed when there is enough space or is replaced by a "hamburger" menu on smaller screens.

This result is achieved very simply by using the standard Bootstrap code to create a navigation bar:

<nav class="navbar navbar-expand-lg">
  <a class="navbar-brand" href="/">Home</a>
  <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>
  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item">
        <a class="nav-link" href="/one">One</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="/two">Two</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="/three">Three</a>
      </li>
    </ul>
  </div>
</nav>

In Windows, the navigation bar is fully displayed with the entries "Home", "One", "Two" and "Three". When emulating a smartphone, only the "Home" menu appears with a hamburger "icon" next to it. Clicking on it brings up a submenu with the choices "One", "Two" and "Three".

Clicking on the hamburger menu changes the div#navbarSupportedContent tag and adds a "show" class (after a very slight animation).

<div class="collapse navbar-collapse show" id="navbarSupportedContent">
  ...
</div>

Clicking on the hamburger icon again, the submenu disappears because the div#navbarSupportedContent loses its "show" class:

<div class="collapse navbar-collapse" id="navbarSupportedContent">
  ...
</div>

There is a problem...

Currently, this is the only Bootstrap feature I use in this application and it requires the "bootstrap.min.js" script. So, only for one rather ridiculous feature, I have to embed 2 scripts on all my pages:

• jquery-3.4.1.min.js (87 ko)
• bootstrap.min.js (57 ko)

It's a bit of a waste...

Practically, I need jQuery, but only with input forms, because it's ASP.NET MVC and it uses the jQuery Validation plugin. But I don't think it's very ecological to load jQuery in all pages because it's easier and that anyway it's cached after a while. Not to mention the 57 kb of "bootstrap.min.js" which serves me absolutely nothing but on the hamburger menu...

The solution (based on jQuery)

That's why I decided to write my own "navbar-toggler.js" script.

$("button.navbar-toggler").on("click", function(e) {
  var target = $(this).data("target");
  $(target).toggleClass("show");
});

And that's all!

• $("button.navbar-toggler") finds the button used to switch the submenu
• .on("click", ...) handles the click on this button
• $(this) finds the clicked button
• .data("target") finds the value of its attribute "data-target" (i.e. "#navbarSupportedContent" in this case)
• $(target) finds the div containing the sub-menu
• .toggleClass("show") adds or removes the "show" class from this div, which allows you to show or hide it

I could stick to $("#navbarSupportedContent").toggleClass("show") since the value of "data-target" will never change, but since the attribute is defined, you might as well use it...

The important and good thing is that I didn't "create" a new hamburger menu system or anything else. I simply use all the HTML and CSS part that Bootstrap 4 offers. Thus, I get all the responsive side that goes with this navigation bar and that fits perfectly to my usage.

Bonus: the animation part is lost when displaying / hiding the hamburger menu, but it's way better for my blood pressure.

The same solution (based on Vanilla JS)

To be perfect, this tiny script should not even rely on jQuery. So that's what I'm going to do now.

document.querySelectorAll("button.navbar-toggler")[0].addEventListener("click", function (event) {
  var target = this.getAttribute("data-target");
  var subbar = document.querySelectorAll(data_target)[0];
  subbar.className = (subbar.className + " show").replace(/ show show/, "");
});

It's literally the same!

• document.querySelectorAll("button.navbar-toggler")[0] finds the button used to switch the submenu
• .addEventListener("click", ...) handles the click on this button
• this retrouve le bouton cliqué
• .getAttribute("target") finds the value of its "data-target" attribute
• document.querySelectorAll(data_target)[0] finds the div containing the sub-menu
• (subbar.className + " show").replace(/ show show/, "") adds or removes the "show" class from this div, which allows you to show or hide it

The final "js-navbar-toggler.js" source code

This gives the following source file, ready to be integrated with a <script src="/js/js-navbar-toggler.js"></script> :

// Vanilla JS navbar toggler for Bootstrap 4
// Source: https://blog.pagesd.info/2019/12/09/gerer-menu-hamburger-bootstrap-vanilla-js

(function () {
  "use strict";

  document.querySelectorAll("button.navbar-toggler")[0].addEventListener("click", function (event) {
    var target = this.getAttribute("data-target");
    var subbar = document.querySelectorAll(target)[0];
    subbar.className = (subbar.className + " show").replace(/ show show/, "");
  });

})();