Javascript is a ... script language. It does not require compilation neither packaging to be released. This doesn't mean developping a javascript library does not require some tooling.
Javascript developers have created nice tools, like jsunit or jsdocs to get a productive and controlled development environment. They also use dedicated libraires like log4javascript for development purpose, split code into fine grained scripts and use some assembly tools to create the released scripts.
The Javascript maven plugin integrates those tools and provide a maven packaging with a dedicated lifecycle.
Many javascript libraries are built based on a set of simple source scripts, dedicated to a particular scope. In many case, using an object orientend javascript style, every javascript class has it's own source file.
The javascript developper don't want to make web developers life complicate and package there code into single scripts, or use-case related scripts, so that only one script import in HTML pages is required to get the library.
Assembling the source scripts can be handled by the javascript maven plugin, either via it's native XML format, or using a jsbuilder assembly file. To avoid confusion with the maven-assembly-plugin , such files are called "assembler descriptors".
A typical assembler looks like this :
<?xml version="1.0"?>
<assembler>
<scripts>
<script>
<fileName>prototype.js</fileName>
<includes>
<include>builder.js</include>
<include>controls.js</include>
<include>dragdrop.js</include>
<include>effects.js</include>
<include>global.js</include>
<include>slider.js</include>
</includes>
</script>
</scripts>
</assembler>
Coding javascript is difficult due to the lack of compiler to check the code, and fiew debuggers availables. Many developers use debuging code, for example based on the log4javascript library.
In some case a production-mode is considered and disables debugs. For example, the log4javascript library comes with a stub version that does nothing. The javascript-maven-plugin offers an alternative solution with the strip-debugs goal. This goal removes all lines from the packaged scripts that start with a special token, by default ";;;". This will remove from the following sample all references to log4javascript :
;;; var logger = log4javascript.getDefaultLogger();
var format = function( n, format )
{
;;; logger.debug( "format " + n + " as " + format );
if( isNaN(n) ) return "-";
....
The compress goal is used to compress web application scripts before packaging a web application. The compressor used is configurable, with support for JsMin , and Dojo Shrinksafe .
The compress-attached goal is for pure javascript developers purpose. It creates a second artifact for the javascript library with compressed scripts.