Drupal has specific ways for working with Javascript, whether it's including files through drupal_add_js() or keeping your site structured with the Libraries. If you don't learn the correct techniques, you'll pay the consequences down the road.

1. Drupal.js
Best Practices
for managing
Javascript in
Drupal
By Bryan Braun

5. The Right Way!
In the .info file
scripts[] = js/example.js
In PHP code:
drupal_add_js('js/example.js')
FYI, drupal_add_js() was removed in Drupal 8.

6. Only load it
when you need it

7. Working With drupal_add_js()
Performance
Defer: TRUE
Every Page: TRUE
Scope: footer
Type: external
Cache: TRUE
drupal_add_js('js/example.js'
drupal_add_js('//cdnjs.clo
drupal_add_js('js/example.js' '
drupal_add_js('js/example.js
array('defer' => 'TRUE'));
udflare.com/ajax/libs/d3/3
array('every_page' 'footer'));
array('scope' => => 'TRUE'));
.4.1/d3.min.js',
<script src='example.js'
Preprocess: TRUE
'external');
defer></script>

8. Working With drupal_add_js()
Load Order
scope
group
every_page
weight
drupal_add_js('js/example.js',
array('group' => 'JS_LIBRARY’));

10. Passing data from PHP to JS
In myModule.module
drupal_add_js(array('myModule'
=> array('key' => 'value')),
'setting');
In example.js
var myValue =
Drupal.settings.myModule.key;

11. Drupal Behaviors
Drupal 7
6
(function ($) {
Drupal.behaviors.example function (context) {
Drupal.behaviors.example = = {
$('.example', context).click(function () {
attach: function (context, settings) {
//$('.example', context).click(function () {
Do things here.
});
// Do things here.
}
});
}
};
})(jQuery);

12. Working With Libraries
Before
After

13. Working With jQuery
The “newer version problem”
jQuery Update jQuery Multi
Drupal 6 -> jQuery 1.2.6 -> 1.3.2
Drupal 7 -> jQuery 1.4.4 -> 1.8.2
Drupal 8 -> jQuery 2.0?
Uses jQuery noConflict*
Updates
Core
-> 2.1.0+
-> 2.1.0+
Alongside
Core*

14. Questions?
@bryanebraun