Content assist with org.eclipse.wst.jsdt.ui.javaCompletionProposalComputer for Eclipse JSDT gives no proposal.
In Preferences -> JavaScript -> Editor -> Content Assist -> Advanced
"Nodeclipse Proposals" are visible, and selected.
as advised by Bananaweizen to Content assist for Eclipse JSDT based Editor
in plugin.xml
<extension point="org.eclipse.wst.jsdt.ui.javaCompletionProposalComputer"
   id="nodeclispe_textual_proposals"
   name="Nodeclipse Text Proposals">
   <proposalCategory icon="icons/npm/npm.gif"/>
 </extension>
 <extension point="org.eclipse.wst.jsdt.ui.javaCompletionProposalComputer"
   id="NodeclipseProposals"
   name="Nodeclipse Proposals">
   <javaCompletionProposalComputer
      class="org.nodeclipse.ui.contentassist.JSDTProposalComputer"
      categoryId="org.eclipse.ui.texteditor.textual_proposals">
      <partition type="__java_javadoc"/>
   </javaCompletionProposalComputer>
 </extension>
JSDTProposalComputer is just wrapper for NodeContentAssistant
(that implements IContentAssistProcessor), that works perfectly well for TextEditor based Editor.
public class JSDTProposalComputer implements IJavaCompletionProposalComputer {
    IContentAssistProcessor assistant = new NodeContentAssistant();
    @Override
    public List<ICompletionProposal> computeCompletionProposals(ContentAssistInvocationContext context, IProgressMonitor monitor) {
        return Arrays.asList(assistant.computeCompletionProposals(context.getViewer(), context.getInvocationOffset()));
    }
    @Override
    public List<IContextInformation> computeContextInformation(ContentAssistInvocationContext context, IProgressMonitor monitor) {
        return Arrays.asList(assistant.computeContextInformation(context.getViewer(), context.getInvocationOffset()));
    }
examples from help are
- HippieProposalComputer - http://svn.codespot.com/a/eclipselabs.org/mobile-web-development-with-phonegap/tags/r1.2/org.eclipse.wst.jsdt.ui/src/org/eclipse/wst/jsdt/internal/ui/text/java/HippieProposalComputer.java
 - HippieProposalProcessor - http://grepcode.com/file/repository.grepcode.com/java/eclipse.org/3.5.2/org.eclipse.ui.workbench/texteditor/3.5.1/org/eclipse/ui/texteditor/HippieProposalProcessor.java
 
All code is on GitHUb contentassist package https://github.com/Enide/nodeclipse-1/tree/master/org.nodeclipse.ui/src/org/nodeclipse/ui/contentassist
