Template:Px/doc

The px meta-template assists other templates, such as infoboxes, to handle image-size parameters given values with or without the unit "px". It takes up to three parameters and returns the first one that has any content. That is, the first one that is defined (not null) and not empty. Thus a default value for the width of the image can be fed as the second or third parameter.

Parameters
{ "description": "Meta-template: ensure ‘px’ unit with numbers for image sizes", "params": { "1": {   "label": "pixels", "description": "add ‘px’ to number, correct format is left unchanged", "type": "number", "aliases": ["2", "3"] } }}

Usage
Here is what this template does. Code to the left, actual rendering to the right:



And with an optional second or even third parameter to be used as a default value if the first or second parameter is empty or undefined:





And here is how it can be used inside another template:



Note! The parameters to must use the pipe "|", like this:. Or else will be fed and return the string " " if width was not defined.

Background
It used to be a bit tricky to handle empty but defined image size values in a template, since the MediaWiki pipetrick doesn't return the default value for empty parameters. That is,  does not return "250px" if the template was called like this:

The usual workaround was to do like this:

When at the same time handling the "pxpx" bug this became even more messy code:

To simplify the coding, px now allows for an optional default value to be defined allowing for the following:



The pxpx bug
Old usage was to always pad on "px" since MediaWiki used to understand "40px" and "40pxpx", but not "40":



But after 25 March 2008 that did not work anymore. That is, image sizes on Wikipedia needed to be given in the form "40px", not "40" or "40pxpx". This template helps doing that. Note that the bug has since been fixed, so MediaWiki now understands "40px" and "40pxpx" again. But MediaWiki still does not understand "40".

But feel free to continue using this template since it is more convenient to use than the old methods.

Alternative approach
Instead of letting your template take say the parameters image and size, you can build your template so it takes an image with full wiki notation. Like this:

This approach is used with many templates, for instance the ambox and dmbox. This gives the users much more freedom in what they feed as the image parameter, and even allows such things as feeding two images at the same time. And it makes your template code much simpler.

Test examples



 * = Example.png


 * = Example.png
 * Fails, MediaWiki does not understand "50" and just thinks it is an image caption.


 * = Example.png
 * Used to fail. But the devs added back parsing of "pxpx". So you should see a small image to the right without any image caption, since Wikipedia again accepts "pxpx".


 * = Example.png
 * = Example.png
 * = Example.png
 * = Example.png
 * = Example.png
 * = Example.png
 * = Example.png
 * Giving the default width if the 1st parameter is empty


 * = Example.png
 * = Example.png
 * Fails to use the default value of 50. Note the missing "|" in.


 * = Example.png