Maintain Readability for Conditional Assignments with JavaScript IIFEs

Very cool. I too often reach for the nested ternary, because I like that it's an expression, despite knowing that it can be hard to reason about. The IIFE definitely works as a good replacement.

However, I also find myself using nested ternaries because I don't like all the "noise" that comes with if-else blocks. Looking at your example, I thought about this for a bit, and wondered, since we're simply checking a conditional and returning a value, maybe something like this inside the IIFE could work as well:

const greeting = (() => {
  const roomStatuses = [
    [isJoiningRoom, 'Welcome'],
    [isLeavingRoom, 'Goodbye'],
    [isEnteringRoom, 'Welcome back'],
    [true, 'Hi'],
  ]
  const roomStatus = roomStatuses.findIndex((element) => element[0])
  return roomStatuses[roomStatus][1]
})()

The logic getting the roomStatus value takes a second to understand versus reading through the if-else block, but I think the readability provided by the roomStatuses array could make it a worthwhile compromise.

Or, if the room status were being tracked as a string, instead of one of several Booleans, we could simplify it a bit with an object literal:

let roomStatus = 'isEnteringRoom'

// See: Replacing switch statements with Object literals | Todd Motto
//   https://toddmotto.com/deprecating-the-switch-statement-for-object-literals/
const greetingFromObject = (() => {
  const roomStatuses = {
    isJoiningRoom: 'Welcome',
    isLeavingRoom: 'Goodbye',
    isEnteringRoom: 'Welcome back',
    default: 'Hi',
  }
  return roomStatuses[roomStatus] || roomStatuses['default']
})()

Here's a jsfiddle of these two implementations in action: Conditional Assignments

Thank you for the inspiration! :)

You could convert the booleans into strings and use them to index into a lookup like you have above (helper functions from ramda)

// booleans
const
isJoiningRoom = false,
isLeavingRoom = true,
isEnteringRoom = false

const greeting = compose(
  flip(prop)({isJoiningRoom: 'Welcome', isLeavingRoom: 'Goodbye', isEnteringRoom: 'Welcome back', 
    default: 'Hi', }),
  propOr('default', 'true'),
  invertObj
)({isJoiningRoom, isLeavingRoom, isEnteringRoom}) // turn the variables into keys which are strings