how to dynamically update data

hi all,

I wanted to get dynamically data from the database when i am making a new invoiceif customer exists, then when i type the first few words, 
I wanted the names in the drop down listif the name is not there, then under the same drop down list, there should also be an option to create a new customer.Similarly I wanted the same for adding products in the invoice.Can you help me here.?I am using codeigniter3 with PHP7I have also attached the pics of what i want.

Please help !!

  createproduct.png (Size: 24.34 KB / Downloads: 11)

  createcompany.png (Size: 20.53 KB / Downloads: 10)