"Created By" field to set up defaults for vlookups/dropdowns

Question

Hello,
I am working on my firm's sharepoint 2013 site and have a custom list that I am trying to make easy for users to use. One of the things I am trying to do is to set default values for some of the dropdown/vlookup columns based on the user who is creating
the new entry.
So let's say I create a list in the site that will contain these two columns:
User    Business Unit
A         Accounting
B         Manufacturing
The user column will match my big list's created by names that are automatically generated. In the big list I will have a Business Unit column that will be matching the values from above. The users should be able to select for which Business Unit they are
doing the work for but majority of the time they will have a default one. 
My goal is to have user A, when creating a new entry to have Business Unit automatically set to Accounting, but also for that user to be able to change it to Manufacturing if needed. This should only apply for creating the item. 
Any ideas how this can happen if at all? I searched all over for this, but can't find an example of how exactly to do it. As a side note, I cannot install any add-ons since I don't have permissions but can write script web parts if that is needed. 
Thank you in advance

Answer 1

Hi,
Per my understanding, you might want to set default value for the “Business Unit” column by looking up to another list.
You can apply
JavaScript with Client Object Model to the NewForm.aspx page to meet your requirement.
A possible solution can be like this: When user opens the NewForm.aspx page of the current list, the custom JavaScript will be executed to get information about the
current user, then query the other list for the default value, set the value to the drop down list of the “Business Unit” column dynamically. The JavaScript can be added into a Content Editor Web Part and insert into the NewForm.aspx page.
The links below would be helpful for implementing this scenario:
About how to
select an option of drop down list using JavaScript:
http://www.imranulhoque.com/javascript/javascript-beginners-select-a-dropdown-option-by-value/
About
how to use JavaScript Client Object model to access SharePoint list:
How to: Create, Update, and Delete List Items Using JavaScript
http://msdn.microsoft.com/en-us/library/office/hh185011(v=office.14).aspx  
Common Programming Tasks in the JavaScript Object Model
http://msdn.microsoft.com/en-us/library/office/hh185015(v=office.14).aspx
Here are two links about how to
add code into SharePoint page via Content Editor Web Part:
http://blogs.msdn.com/b/sharepointdev/archive/2011/04/14/using-the-javascript-object-model-in-a-content-editor-web-part.aspx
http://sharepointadam.com/2010/08/31/insert-javascript-into-a-content-editor-web-part-cewp/
Best regards
Patrick Liang
TechNet Community Support