问题:

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.

回答1:

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.

回答2:

I faced the same problem when I tried to install Angular.js with bower in my project. I seems bower has lots of javascript files it downloaded automatically which caused my IDE to stuck in validation process for a long time. So, I solved this problem this way,

I first installed tern.js 0.9.0.
Then I went to the project properties, selected tern script path included only the path I needed for validation, My project's javascript folder. I excluded other path like placeholders, Angular.js files, Jquery files.
I selected the Javascript from the properties again and did the same things in include path's source.

My IDE currently working without freezing. I took help from there. Tern I guess it can be helpful, where any IDE stuck due to lots of Javascript file.