Add an extra field to a form

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I have a form that adds items to the database. What i'm trying to do is to also allow the user to add multiple values for a category.

 

Say for example i have a field name locations...

 

i want the user to add multiple locations.

 

The locaions are on a Select form field and the values are being retrieved from the database.

 

so how could have a link below the select field that says "add another location" and display another select form field.

 

I was thinking something like <a href="index.php?action=addnewLocation">Add another location</a>

 

The problem like i mentioned is that i want it use ajax and add it automatically, or use another method.