The best way I've found to to set a variable based on multiple conditions

best-conditional.js

//In helper file with global helper functions
function switchMap(before_value, map={}, default_value=false){
  return Object.keys(map).includes(before_value) ? map[before_value] : default_value;
}

//In code where condition is needed
var friendly_timezone = switchMap(tz_timezone, {
  'America/New_York': 'Eastern',
  'America/Chicago': 'Central',
  'America/Denver': 'Mountain',
  'America/Los_Angeles': 'Pacific',
}, "No Timezone Specified");