Global variable defined in function appears not defined?

Question

I\'m writing a script for Google Spreadsheets, I want to have my headers index available globally throughout the script.

According to the theory, I should be able to def

Answer 1

I've found a solution I believe, but I'm not sure it is the "proper" way to do this.

I'm simply defining the global variable above in the script:

headerNameIndex = SpreadsheetApp.getActiveSheet().getDataRange().getValues()[0].indexOf("First-Last")

Which seems to work.

I had wrongly assumed it would only work if it was defined in the onOpen() function.