Minimize Number of JavaScript Files to Load

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Minimize Number of JavaScript Files to Load


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Overview

ZK loads the required JavaScript files only when it is required. It is similar to Java Virtual Machine's class loader, but ZK's JavaScript loader loads a JavaScript package at once. It minimizes the number of bytes to be loaded to a browser. However, with an Internet connection, a Web page is loaded faster if the number of files to load is smaller (assuming the total number of bytes to transmit is the same).

ZK, by default, loads both zul and zul.wgt packages when the zk package is loaded, since they are most common packages a ZK page might use. A ZK page generally uses more packages than that, and you, as an application developer, can pack them together to minimize the number of JavaScript files.

Notice that the more packages you packed, the larger the file it is. It will then slow down the load time if some of packages are not required. Thus, only packed the packages that will be required by most of users.

Minimize the Number of JavaScript Files for a ZUL Page

In the index.zul of the zkdemo there are about 15 JavaScript files will be loaded at beginning as follows:

 * http://www.zkoss.org/zkdemo/zkau/web/947199ea/js/zk.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/947199ea/js/zul.lang.wpd
 * http://www.zkoss.org/zkdemo/userguide/macros/category.js
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zkmax.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zul.wgt.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zul.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zul.utl.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zul.layout.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zul.wnd.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zul.tab.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zul.inp.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zul.box.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zul.sel.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zk.fmt.wpd
 * http://www.zkoss.org/zkdemo/zkau/web/_zv2010062914/js/zul.mesh.wpd

This means the browser will trigger 15 request to load the 15 JavaScript files, even if each file is not too big, it still takes more time to connect to server to download it. However, we can specify a JSP file to include several JavaScript into one and declare it at the top of the index.zul. For example, (zkdemo.js.jsp)

<%@ page contentType="text/javascript;charset=UTF-8" %>
<%@ taglib uri="http://www.zkoss.org/dsp/web/core" prefix="c" %>
<% org.zkoss.zk.fn.JspFns.setCacheControl(response, null, 24); %>
<c:include page="~./js/zk.fmt.wpd"/>
<c:include page="~./js/zul.mesh.wpd"/>
<c:include page="~./js/zul.utl.wpd"/>
<c:include page="~./js/zul.layout.wpd"/>
<c:include page="~./js/zul.wnd.wpd"/>
<c:include page="~./js/zul.tab.wpd"/>
<c:include page="~./js/zul.inp.wpd"/>
<c:include page="~./js/zul.box.wpd"/>
<c:include page="~./js/zul.sel.wpd"/>
<c:include page="/userguide/macros/category.js"/>

Note:

  1. The included JavaScript file has itself sequence, so you cannot put them randomly.
  2. The zk.wpd is a ZK core Javascript so you don't need to include it
  3. The zul.lang.wpd is an I18N message, so you don't need to include it.
  4. As a new feature introduced in ZK 5.0.4 release(#System-wide_Minimizing_the_Number_of_JavaScript_Files), these package of zul, zul.wgt, and zkmax will be merged automatically into zk package, so you don't specify them into the zkdemo.js.jsp file.
  5. The setCWRCacheControl() method is used to set the Cache-Control and Expires headers for class Web resources.

index.zul

<?page id="userGuide" title="ZK Live Demo"?>
<?script type="text/javascript" src="/userguide/macros/zkdemo.js.jsp?${desktop.webApp.build}"?>
// omitted

As you can see, we append an Expression Language script(${desktop.webApp.build}) at the end of the URI zkdemo.js.jsp, which can solve the browser cache issue when the file has been updated.

System-wide Minimizing the Number of JavaScript Files

[since 5.0.4]

If a package is used by all your pages, you could configure it system wide by specifying the packages in the language addon. Please refer to ZK Configuration Reference/zk.xml/The language-config Element for how to specify a language addon.

For example, if the zul.wnd package (Window) is required for all pages, then you could add the following to the language addon.

<javascript package="zul.wnd" merge="true"/>

Notice that you have to specify the merge attribute which indicates the JavaScript code of the package will be loaded with the zk package. In other words, the ~./js/zk.wpd will contain all the packages specified with the merge attribute.

Also notice that if you use several DSP/JSP file to load multiple packages in a file as described in the previous section, you generally don't specify them here. Otherwise, you will load the same package twice (though it is safe, it wastes time).

Turn Off the Merging of JavaScript Packages

As described above, both zul and zul.wgt packages are merged into the zk package. If you prefer to load them separately, you could disable it by specifying the ondemand attribute as follows.

<javascript package="zul" ondemand="true"/>
<javascript package="zul.wgt" ondemand="true"/>

Notice that all packages are default to load-on-demand, you rarely need to specify the ondemand attribute, unless you want to undo the package that has been specified with the merge attribute.


Last Update : 2010/08/30

Copyright © Potix Corporation. This article is licensed under GNU Free Documentation License.