[javascript] How To Set A JS object property name from a variable

Along the lines of Sainath S.R's comment above, I was able to set a js object property name from a variable in Google Apps Script (which does not support ES6 yet) by defining the object then defining another key/value outside of the object:

var salesperson = ...

var mailchimpInterests = { 
        "aGroupId": true,
    };

mailchimpInterests[salesperson] = true;