jQueryWTP
Eclipse WTP support javascript code content assistance,but does not support jQuery.
jQueryWTP is a tool make Eclipse WTP support jQuery code content assistance.

Download
you can download here.Installations
step1:download jqueryWTP_version.jarstep2:find you Eclipse Plugin org.eclipse.wst.javascript.ui_xxxxxxx.jar,backup the plugin.
step3:double click the jar file or run with command java -jar jqueryWTP.version.jar
step4:on the opened swing UI,choose org.eclipse.wst.javascript.ui_xxxxxxx.jar,and output dir.
step5:click generate button.
step6:replace old org.eclipse.wst.javascript.ui_xxxxxxx.jar file with the generated file.
step7:restart eclipse.
step8:open a html file,edit js content.
Video
How it works
jQueryWTP add Javascript code content assistant config file's to Eclipse Plugin org.eclipse.wst.javascript.ui_xxxxxxx.jar.here is the config snippet copied from the plugin,which make WTP support document.getElementById
#/---------------------------------------
#!getElementById()
#@type=method
#@iesupport=y
#@nssupport=n
#@ecmasupport=n
#@fc=doneclass