useFallback: Reactive nullish coalescing operator

Clear and concise description of the problem

~I want logicalOr, but with the nullish coalescing operator (??).~

I want to write fallback code. As @thedamon pointed out below, nullish coalescing isn’t what we want because we want to be able to short-circuit the fallback with an explicit null.

Context

I’m writing a lot of universal fallback code to check if a user has passed in props.modelValue or props.value so that my component code is backwards compatible.

This ends up with me writing:

const val = computed(() => props.modelValue ?? props.value)

// pass into useVModel(val), etc.

in a lot of components.

Suggested solution

A function called useFallback which would take in args.

Usage

const props = defineProps<{
  someValue: string
  deprecatedValue: string
  defaultValue: string
}>()

const resolvedValue = useFallback(props.someValue,
  props.deprecatedValue,
  props.defaultValue)

Alternative

We could pass in the entire props object and use an Array, like useVModel does.

Additional context

Honestly, I’m just looking for a concise way to declare fallbacks for two values: modelValue and value.

The better solution to my problem is probably to make a feature request to useVModel so that it also handles the emit backwards compatibility.

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn’t already an issue that request the same feature to avoid creating a duplicate.

[thedamon]

The better solution to my problem is probably to make a feature request to useVModel so that it also handles the emit backwards compatibility.

Is there appetite to bake some of the ‘vue-bridge’ type functionality into VueUse? then it could maybe be as direct as useBridgedVModel which would be a separate as necessary but potentially reusing the vueUse function bridgified version of useVModel ?

[JessicaSachs]

That’s a good point. In which case, useFallback isn’t really gonna use the nullish coalescing operator, it will let you short-circuit with an explicit null.

We should open another feature request for logicalNullish or nullish and that’ll go in the @vueuse/math package.