ssrRef, shallowSsrRef

You can define data on the server that is stringified and hydrated on client-side.

When creating composition utility functions, often there will be server-side state that needs to be conveyed to the client.

If initialised within setup() or via onGlobalSetup, ssrRef data will exist only within the request state. If initialised outside a component there is the possibility that an ssrRef may share state across requests.


ssrRef will automatically add ref values to window.__NUXT__ on SSR if they have been changed from their initial value. It can be used outside of components, such as in shared utility functions, and it supports passing a factory function that will generate the initial value of the ref.

import { ssrRef } from '@nuxtjs/composition-api'

const val = ssrRef('')

// When hard-reloaded, `val` will be initialised to 'server set'
if (process.server) val.value = 'server set'

// When hard-reloaded, the result of myExpensiveSetterFunction() will
// be encoded in nuxtState and used as the initial value of this ref.
// If client-loaded, the setter function will run to come up with initial value.
const val2 = ssrRef(myExpensiveSetterFunction)
Under the hood, ssrRef requires a key to ensure that the ref values match between client and server. If you have added @nuxtjs/composition-api/module to your buildModules, this will be done automagically by an injected Babel plugin. If you need to do things differently, you can specify a key manually or add @nuxtjs/composition-api/dist/babel-plugin to your Babel plugins.
At the moment, an ssrRef is only suitable for one-offs, unless you provide your own unique key. More information.


This helper creates a shallowRef (a ref that tracks its own .value mutation but doesn't make its value reactive) that is synced between client & server.

import { shallowSsrRef, onMounted } from '@nuxtjs/composition-api'

const shallow = shallowSsrRef({ v: 'init' })
if (process.server) shallow.value = { v: 'changed' }

// On client-side, shallow.value will be { v: changed }
onMounted(() => {
  // This and other changes outside of setup won't trigger component updates.
  shallow.value.v = 'Hello World'
At the moment, a shallowSsrRef is only suitable for one-offs, unless you provide your own unique key. More information.