CODEWITHSUNDEEP
javascriptperformancewordpress
4thSpace
4thSpace

Reputation: 44352

Does javascript execute if no function is called?

I have some wordpress pages with javascript code that require javascript file references. For pages that don't call functions within these js file references, there should be no performance impact for including these files (except the file call) right?

-- EDIT in response to @cdhowie --

If only certain pages require these javascript files, is it possible to move them out of the head section and into the page? I've read this is bad practice.

But in theory, this prevents the entire site from having a performance hit for files that are not being utilized?

Upvotes: 0

Views: 882

Answers (3)

Devin Lynch
Devin Lynch

Reputation: 289

Javascript functions are only executed when you explicitly call them (or implicitly in callbacks and whatnot). The code will however still be interpreted by the browser on each page regardless of functions being called or not.

Edit: I was wrong to say the performance hit is irrelevant. It really all depends on your exact situation (where the code is coming from, how much code, etc.) and also how much you care about performance in terms of milliseconds.

One possible "performance" issue is if those extra .js files are on your server. If so and you are loading them when it is not needed, you are causing for unneeded traffic and bandwidth in regards to your server.

Upvotes: 1

Marc B
Marc B

Reputation: 360772

This will execute, but take up very little cpu time

<script type="text/javascript">
   // just a comment
</script>

no functions, just a comment... but it's still "code", still has to be parsed, still has to be checked for syntax errors, etc...

Upvotes: 1

cdhowie
cdhowie

Reputation: 169231

The referenced JavaScript files will be downloaded (or fetched from the cache) and then be executed by the browser's JavaScript interpreter in both cases. The "JavaScript file references" need to be executed in order to create the variables and functions that you might use, and the browser has no way of knowing ahead of time if you will use them. Further, the included files might actually manipulate the document, and the browser doesn't know this either until it has executed them.

So yes, there will be a performance impact whether or not you call the functions. Whether or not it's significant enough for you to worry about is something you will have to determine. (Always profile your page's loading time before making decisions like this!)

Upvotes: 3

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