How to do conditional defining of key in an object in JS?

Suppose I want to create an object with keys as USD and non-USD. Like Below:

    let obj = {
                USD: {
                   sourceValue: 100
                   destinationValue: 10
                }, 
                non-USD: {
                  sourceValue: 10
                   destinationValue: 100
                }
              }

Except here, instead of non-USD, I should be able to pass any currency, like SGD or HKD and I should get result of non-USD currency.

so, if I wrote obj[currency].sourceValue and currency=HKD then I should get 10

I don’t want to use obj[1].sourceValue as currency value is dynamic.

Also, I don’t want to use if(currency!='USD') index=1 and then obj[index].sourceValue

So, my question is, what should I write at place of non-USD while defining object? I checked computation names, but I am not sure, how will I pass long currency array as key name and filter USD out of it?