[Vuejs]-String passed to store action (via mapActions) arrives as [object, Object]

Try the following, in the child component pass the id as follows:

this.$emit('remove', this.item.id);

Then, the parent renders the child as follows:

<ListItem v-for="item in listItems" :key="item.id" 
          :item="item"
          @remove="deleteListItem"
/>

methods: {
...mapActions('listItems', ['deleteItem',],),
deleteListItem (id) {
     this.deleteItem(id);
},

It turns out I needed to wrap the argument in an object when I pass it to the store. Doing this.deleteItem({id}); seemed to fix the issue…

the first argument in vuex actions is the context object. If you don’t want to use it and just use the payload you could use it like this:

deleteItem (_, id) {
  api.del(`${deleteURL}/${id}`);
},

more info about context object