compile js file in java project

The most import thing is to let java project know the js builder.

#@#] sudo vi /home/A/myProj/proj_eclipse/src/.project

<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
        <name>BBB</name>
        <comment></comment>
        <projects>
        </projects>
        <buildSpec>
            <buildCommand>
                        <name>org.eclipse.jdt.core.javabuilder</name>  <!-- java builder => java project -->
                <!--    <name>org.eclipse.wst.jsdt.core.javascriptValidator</name> --> <!-- js builder => js project -->
                        <arguments>
                        </arguments>
                </buildCommand>
        </buildSpec>
        <natures>
                <nature>org.eclipse.jdt.core.javanature</nature>  <!-- java builder -->
                <nature>org.eclipse.wst.jsdt.core.jsNature</nature> <!-- js -->
        </natures>
</projectDescription>

Then <Your project>->right click-> Properties -> javascript -> Include Path -> Libraries -> add javascript libaray...

Have fun.