Currently diving into the ExtJs documentation and stumbled upon the BLANK_IMAGE_URL property. According to the docs, it's a link to a 1-pixel transparent GIF that helps with accurate measurements.
But how can such a small image be useful for measuring things? And what makes it so important?
PS: Or is this just an inside joke amongst ExtJs developers? Like, "Haha! Another unsuspecting fool setting BLANK_IMAGE_URL, what a goofball!" :)
ExtJS 2 and 3 installation guidelines suggest hosting the image yourself, while ExtJS 4 has replaced the image with a data uri scheme (
data:image/gif;base64,R0lGODlhAQABAID/AMDAwAAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==The ExtJS 4 documentation provides a clearer explanation:
URL to a 1x1 transparent gif image utilized by Ext to generate inline icons using CSS background images. In older versions of IE, this defaults to "http://extjs.com/s.gif" and should be changed to a URL on your server. For other browsers, it utilizes an inline data URL
This is utilized in functions like setIconCls, where an <img> tag is created with Ext.DomHelper with BLANK_IMAGE_URL as src and the actual icon as background. This simplifies scaling, measuring, and adding dimensions compared to using a <div> or <span> and manipulating their positioning extensively.
// Ext.Panel.setIconClass
setIconClass : function(cls){
// Snip ...
Ext.DomHelper.insertBefore(hdspan.dom, {
tag:'img',
alt: '',
src: Ext.BLANK_IMAGE_URL,
cls:'x-panel-inline-icon '+cls
});
// Snip ...
}
Using a 1px image is a straightforward way to create and fill areas on a webpage. This technique has been around for quite some time. Here's how it works:
When you need a strip (img) to occupy a specific area (div) without collapsing, while also allowing other items to adjust accordingly, instead of using an empty div with fixed dimensions, inserting a 1px image in that div and setting its height and width can be more effective.
Because this image is single-colored at only 1px, stretching it won't result in any loss of quality, serving its purpose well.
The rendering of a Div or any element may vary from one browser to another, making precise consistency challenging across browsers. However, using an Image tag could provide a reliably consistent appearance regardless of the browser being used.
Possibly a tracking pixel, used to collect data on site usage by analyzing access logs for requests made to the pixel and its referer.
Check out this blank.gif:
http://en.wikipedia.org/wiki/File:Blank.gif
The significance of this image is likely related to ensuring compatibility with older versions of Internet Explorer.
For more information, see:
BLANK_IMAGE_URL sets the URL for a 1x1 transparent gif image that Ext uses to generate inline icons using CSS background images for certain widgets. By default, it is set as "http://extjs.com/s.gif," but you should customize it to a URL on your own server.
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