Javascript Event Values

Hello community,

I'm hoping someone might be able to help me with a script I'm trying to write.  I have (3) fields of text information (First, M, Last) and when someone fills in each section on the form my goal is to populate those inputs into one field somewhere else on the form.

Field 2a = First

Field 3a = M

Field 4a = Last

I know that "event.value=this.getField("2a").value" will give me the value that is in Field 2a.  I just don't know how to put them together into one field and so there is a space in between.  

Any help or suggestions would be much appreciated!

Thank you in advance.