Vue.js 3 - replace/update reactive object without losing reactivity

Question

I need to update a reactive object with some data after fetching:

  setup(){
    const formData = reactive({})

    onMounted(() => {
      fetchData().then((data) => {
        if (data) {
          formData = data //how can i replace the whole reactive object?
        }
      })
    })
  }

formData = data will not work and also formData = { ...formdata, data }

Is there a better way to do this?

Answer 1

According to the official docs :

Since Vue's reactivity tracking works over property access, we must always keep the same reference to the reactive object. This means we can't easily "replace" a reactive object because the reactivity connection to the first reference is lost

reactive should define a state with nested fields that could be mutated like :

 setup(){
    const data= reactive({formData :null })

    onMounted(() => {
      fetchData().then((data) => {
        if (data) {
          data.formData = data 
        }
      })
    })

  }

or use ref if you just have one nested field:

  setup(){
    const formData = ref({})

    onMounted(() => {
      fetchData().then((data) => {
        if (data) {
          formData.value = data 
        }
      })
    })

  }