Trying to replicate an excel formula in a form

Hello all,

In Excel, I had a dropdown cell and then other cells throughout the page linked to item selected in the dropdown to change based on the selection.  In practice it's a simple IF THEN statement, however I'm having trouble replicating this in JavaScript.

For example, if the dropdown box choices are (Gold, Silver, Copper), then I need a separate textbox to populate with (150,100,50) respectively, and then another separate textbox still linked to the dropdown choice to populate with (A,B,C) etc and so on throughout the page as needed, all hinging on the dropdown choice selected.

This is what I used in Excel, is this possible to replicate?

  =IF($I$12="Gold",150,IF($I$12="Silver",100,IF($I$12="Copper",50,IF($I$12="________",0))))

Any advice or direction would be appreciated.  Thank you.

Eric