Function computed

Takes a getter function and returns a readonly reactive ref object for the returned value from the getter. It can also take an object with get and set functions to create a writable ref object.

Example

// Creating a readonly computed ref:
const count = ref(1)
const plusOne = computed(() => count.value + 1)

console.log(plusOne.value) // 2
plusOne.value++ // error

// Creating a writable computed ref:
const count = ref(1)
const plusOne = computed({
  get: () => count.value + 1,
  set: (val) => {
    count.value = val - 1
  }
})

plusOne.value = 1
console.log(count.value) // 0

See

https://vuejs.org/api/reactivity-core.html#computed