vuex/docs/en/forms.md

Form Handling

When using Vuex in strict mode, it could be a bit tricky to use v-model on a piece of state that belongs to Vuex:

<input v-model="obj.message">

Assuming obj is a computed property that returns an Object from the store, the v-model here will attempt to directly mutate obj.message when the user types in the input. In strict mode, this will result in an error because the mutation is not performed inside an explicit Vuex mutation handler.

The "Vuex way" to deal with it is binding the <input>'s value and call an action on the input or change event:

<input :value="message" @input="updateMessage">

// ...
vuex: {
  state: {
    message: state => state.obj.message
  },
  actions: {
    updateMessage: ({ dispatch }, e) => {
      dispatch('UPDATE_MESSAGE', e.target.value)
    }
  }
}

And here's the mutation handler:

// ...
mutations: {
  UPDATE_MESSAGE (state, message) {
    state.obj.message = message
  }
}

Admittedly, this is quite a bit more verbose than a simple v-model, but such is the cost of making state changes explicit and track-able. At the same time, do note that Vuex doesn't demand putting all your state inside a Vuex store - if you do not wish to track the mutations for form interactions at all, you can simply keep the form state outside of Vuex as component local state, which allows you to freely leverage v-model.