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Legacy Libraries & global jQuery

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Now that layout.js is being processed through webpack, we can remove our self-executing function and replace the $ with const $ = require('jquery'):

'use strict';
const $ = require('jquery');
$(document).ready(function() {

We rock! But this time... there's a surprise. When we refresh, we do not get warm, fuzzy feelings: we get a cold and not-so-fuzzy error:

$.tooltip() is not a function


8 lines | web/assets/js/layout.js
// ... lines 1 - 4
$(document).ready(function() {

This $.tooltip() function should be coming from Bootstrap... which is included in our base layout:

110 lines | app/Resources/views/base.html.twig
// ... lines 1 - 98
{% block javascripts %}
// ... line 100
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
// ... lines 102 - 105
{% endblock %}
// ... lines 107 - 110

So... why isn't this working? Well... think about it: Bootstrap's job is to modify jQuery and add more functions to it, like "tooltip". But, in layout.js, we require a different, fresh, unmodified jQuery and then try to call .tooltip() on it!

8 lines | web/assets/js/layout.js
// ... lines 1 - 2
const $ = require('jquery');
$(document).ready(function() {

That doesn't work because - when the Bootstrap code is loaded - it modifies the jQuery that's loaded in our layout: it modifies the global jQuery variable. In layout.js, we're not using the global jQuery variable: we're requiring our own jQuery... which has not been modified by Bootstrap.

The fix? We already know it: we need to once again handle all our dependencies inside layout.js. I mean, if we need bootstrap functions inside of this file, then we need to require bootstrap here.

Let's do it!

Installing and Requiring Bootstrap

First, install Bootstrap:


Hey, Bootstrap 4 is out! But this site is designed for Bootstrap 3 CSS, so don't forget to change your dependency to version 3: yarn add bootstrap@3 --dev.

yarn add bootstrap@3 --dev

Then, in layout.js, this is interesting: just say require('bootstrap'):

9 lines | web/assets/js/layout.js
// ... lines 1 - 2
const $ = require('jquery');
// ... lines 5 - 9

Nope, I'm not setting this to a variable. This is really common with jQuery plugins, like Bootstrap. These files don't actually return anything. Instead, we require them so that they modify the jQuery function and add new functions to it.

We should be good, right? Try it! Ah!!! The same cold, unfuzzy error! This is confusing.

Modules that Rely on Global Variables

To see what's really going on, open the base layout and remove the script tags for jQuery and bootstrap:

108 lines | app/Resources/views/base.html.twig
// ... lines 1 - 98
{% block javascripts %}
<script src="{{ asset('bundles/fosjsrouting/js/router.js') }}"></script>
<script src="{{ path('fos_js_routing_js', { callback: 'fos.Router.setData' }) }}"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/es6-promise/4.0.5/es6-promise.auto.min.js"></script>
<script src="{{ asset('build/layout.js') }}"></script>
{% endblock %}
// ... lines 105 - 108

We don't need these anymore: we've refactored all of our code to properly require what we need instead of relying on global variables.

And when we refresh now, the new error is a bit more helpful:

jQuery is not defined

The source of this isn't clear at first, but this is coming from Bootstrap. This is where Webpack gets tricky.

The bootstrap module relies on there to be a global jQuery variable. Yep, it's behaving poorly.

Look, in a perfect world, when we require bootstrap, internally, it would use the require() function to require jQuery and then modify it. See, if multiple files require the same module - like jQuery, they are all returned the same object. This means that Bootstrap would add the tooltip() function to the same jquery that we use in layout.js.

But.... that doesn't happen. Instead, Bootstrap looks for a global jQuery variable to modify. If there is no global variable - like in our nice system - it explodes.

Fixing Poorly-Behaving Modules

There are a few ways to fix this. First, we could say window.jQuery = $ before requiring bootstrap. If we try that and refresh, no more errors! Yep, we require the jquery module and then make it a global variable just in time for Bootstrap to look for it.

But there are a few problems with this... the biggest being that I don't want to keep relying on global variables! And second... we're probably going to face this issue again and again... with other jQuery plugins. I'd rather have a more global way of fixing this.

How? Through the power of Webpack!