Question

97

What is the danger in including the same JavaScript library twice?

rated 0 times [ 102] [ 5] / answers: 1 / hits: 18463 / 14 Years ago, thu, february 3, 2011, 12:00:00

One of the webapps I'm working in is made up of many partial HTML files. If the partial requires a JavaScript library such as YUI, the YUI library is included in the partial.

When the partials are combined at runtime, the resulting HTML often includes the YUI library several times.

<html>

... 

<script type=text/javascript src=/js/yahoo/yahoo-min.js></script>

... 

<script type=text/javascript src=/js/yahoo/yahoo-min.js></script>

... 

<script type=text/javascript src=/js/yahoo/yahoo-min.js></script>

...

</html>

I've seen strange behavior from including jQuery several times, especially when using AJAX. Why, specifically, is including the same JavaScript library more than once a bad idea? Why does it only sometimes cause problems?

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answered 14 Years ago robertjaysona · Accepted Answer

Depending on the library, including it more than once could have undesired effects.

Think of it like this, if you have a script that binds a click event to a button, and you include that script twice, those actions will be ran twice when the button is clicked.

You could write a simple function that you call to load a script and have it keep track of files that have already been loaded. Or, I'm sure you could probably use a pre-existing JS loader such as LabJS and modify it.