chrome.storage.local.set using a variable key name

In a Google Chrome Extension, I want to use chrome.storage.local (as opposed to localStorage) because:

1. With key-value pairs, the value can be any object (as opposed to string only)
2. Changes to the data model using setter storage.set can trigger an event listener

Using storage.set, how can I have a variable key name?

Note: If I don't use the setter, I can do storage[v1], but changes to the object won't trigger the event listener.

var storage = chrome.storage.local;
var v1 = 'k1';

storage.set({v1:'s1'});

storage.get(v1,function(result){
    console.log(v1,result);
    //console output = k1 {}
});
storage.get('v1',function(result){
    console.log(result);
    //console output = {v1:'s1'}
});