When running Eclipse Kepler and importing an existing Maven project, Eclipse hangs during "Building Workspace (XX%)". Switching to the Progress tab reveals a "Validating nnn"; it looks like it’s validating a directory containing JavaScript files.
Kill Eclipse process.
Go to project folder and edit .project file.
Remove the following lines (it will disable failing JavaScript validator):
<buildCommand>
<name>org.eclipse.wst.jsdt.core.javascriptValidator</name>
<arguments>
</arguments>
</buildCommand>
Save file.
Re-open Eclipse.