Updating state of vuex array when one item has some changes

Question

I have an array called cases in my vuex store.

I want to update the array with the new content when I update a few fields within an existing item in the array.

I thought I could do something like this in my mutation but doesn't work and get the error typeError: undefined is not an object (evaluating 'state.objects.find') —

EDIT_CASE (state, payload) {     const item = state.objects.find(item => item.id === payload.recordId); Object.assign(item, payload.case_status); 

my array is as follows:

[     {         "case_name": "Laptop not working",         "case_status": "live",         "case_summary": "This is some summary content",         "createdBy": "zippy",         "createdDate": "2018-06-21T15:20:22.932Z",         "id": "-LFXvk9yY5c-O8yIdf8k"     },     {         "case_name": "Something else",         "case_status": "live",         "case_summary": "This is some summary content",         "createdBy": "zippy",         "createdDate": "2018-06-21T15:20:22.932Z",         "id": "-STVvk9yY5c-O3yiTy8k"     } ] 

I also think from what I have read Vue does not observe changes within arrays so it may be I'm going completely the wrong way with this, and need to remove and then re-add the array item?

Basically I have a list, I make a change to my backend, now I want that list to reflect the changes I have made through updating the cases state, can anyone help?

Answer 1

There is no array issue with your example because you try to change an object property - not array element reference. The problem is in Object.assign(item, payload.case_status); - you should provide an object not just a field. (Also you said that array called cases but example has objects, maybe this is problem too);

So this should work:

EDIT_CASE (state, payload) {     const item = state.objects.find(item => item.id === payload.recordId);     Object.assign(item, payload); } 

The error:

undefined is not an object

I think, it is related to Object.assign because you pass field to it which is undefined probably.

P.S. There is small example to help you understand when array issue appears and when everything works fine. See code comments :)

new Vue({    el: "#app",    data: {      todos: [        { text: "Learn JavaScript" },        { text: "Learn Vue" },        { text: "Play around in JSFiddle" },        { text: "Build something awesome" }      ]    },    methods: {      // work because object property is reactive    	changeItemProperty() {      	this.todos[3].text = "changedItemProperty";      },      // same reason, properties are reactive      changeItemWithAssign() {      	Object.assign(this.todos[3], { text: "changedItemWithAssign" });      },      // does not work, can not track changes in array      // also this will break all attempts to change TEXT property in UI      // because property becomes not reactive after this due to new object      // try to changeItemProperty or  changeItemWithAssign - does not work!      // changeItem2 will fix it :)      changeItem() {      	this.todos[3] = { text: "changedItem" }      },      // works      changeItem2() {      	Vue.set(this.todos, 3, { text: "changedItem2" });      }	    }  })

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.16/vue.min.js"></script>  <div id="app">    <div v-for="todo in todos" :key="todo.text">       {{todo.text}}    </div>    <button @click="changeItemProperty">changeItemProperty(works)</button>    <button @click="changeItemWithAssign">changeItemWithAssign(works)</button>    <button @click="changeItem">changeItem(does not work!)</button>    <button @click="changeItem2">changeItem2(works)</button>  </div>

Answer 2

JavaScript (not specific to Vue) can not detect setting the value of an Array item directly by index arr[3] = 'stop'; It also can not detect adding a new key or deleting an existing key from an Object. You must be defining the initial state of the store, e.g.

const store = new Vuex.Store({   state: {     objects: []   },   mutations: {     EDIT_CASE (state, payload) {       const index = state.objects.findIndex(item => item.id === payload.id);       if (index !== -1) state.objects.splice(index, 1, payload);     }   } })