Solving the 'never' type issue in Vue3 and TypeScript for an empty array reference

Question

Solving the 'never' type issue in Vue3 and TypeScript for an empty array reference

I am currently in the process of migrating a component from an old Vue project that relies solely on JavaScript to a TypeScript/Vue project, and I have encountered some obstacles along the way.

<script lang="ts">
import { computed, ref } from "vue";
import { defineComponent } from 'vue'
export default defineComponent ({
setup() {

const todo = ref("");
const todos = ref([]);
let id = 0;
const numberOfCompletedTodos = computed(
  () => todos.value.filter((todo) => todo.completed).length
);
function addTodo() {
  todos.value.push({
    id: id,
    title: todo.value.trim(),
    completed: false,
  });
  todo.value = "";
  id++;
}
function removeTodo(index) {
  todos.value.splice(index, 1);
}
...
...
...
</script>

However, the use of ref([]) is resulting in the following errors:

- Argument of type '{ id: number; title: string; completed: boolean; }' is not 
assignable to parameter of type 'never'.ts(2345)

- Property 'completed' does not exist on type 'never'.

- Parameter 'index' implicitly has an 'any' type.

typescript vue.js vuejs3

Answer 1

Answer №1

When using the ref function, it has the ability to determine the type of the value you want to store in the reference that is returned. If you pass in an empty array, the inferred type becomes never[], indicating an array that will never contain any elements. Obviously, this is not the desired outcome. One way to fix this is by initializing the ref with an array containing Todo objects, but this may not be the best approach.

To accurately specify that you intend to store Todos in the array, TypeScript requires a type parameter when calling the ref function. You can achieve this by creating a type or an interface for Todo and passing it like so:

type Todo = {
  id: number;
  title: string;
  completed: boolean;
}

const todos = ref<Todo[]>([]);

Alternatively, you can define the type inline as shown below:

const todos = ref<{ id: number; title: string; completed: boolean }[]>([]);

Answer 2

When using the ref function, it has the ability to determine the type of the value you want to store in the reference that is returned. If you pass in an empty array, the inferred type becomes never[], indicating an array that will never contain any elements. Obviously, this is not the desired outcome. One way to fix this is by initializing the ref with an array containing Todo objects, but this may not be the best approach.

To accurately specify that you intend to store Todos in the array, TypeScript requires a type parameter when calling the ref function. You can achieve this by creating a type or an interface for Todo and passing it like so:

type Todo = {
  id: number;
  title: string;
  completed: boolean;
}

const todos = ref<Todo[]>([]);

Alternatively, you can define the type inline as shown below:

const todos = ref<{ id: number; title: string; completed: boolean }[]>([]);

Answer 3

Answer №2

To streamline the process, I would suggest creating an interface specifically for this purpose. Additionally, utilizing the generic ref<> can simplify things.

ITodoInterface.ts

export interface ITodoInterface {
        id: number;
        title: string;
        completed: boolean;
    }

TodoComponent.vue

<script lang="ts">
import { computed, ref } from "vue";
import { defineComponent } from 'vue'
export default defineComponent ({
    setup() {
        const todo = ref<ITodoInterface|undefined>(undefined);
        const todos = ref<ITodoInterface[]>([]);
        let id = 0;
        const numberOfCompletedTodos = computed(
            () => todos.value.filter((todo) => todo.completed).length
        );
        function addTodoItem() {
            todos.value.push(todo.value);
            todo.value = undefined;
            id++;
        }
        function removeTodoItem(index) {
            todos.value.splice(index, 1);
        }
</script>

Answer 4

To streamline the process, I would suggest creating an interface specifically for this purpose. Additionally, utilizing the generic ref<> can simplify things.

ITodoInterface.ts

export interface ITodoInterface {
        id: number;
        title: string;
        completed: boolean;
    }

TodoComponent.vue

<script lang="ts">
import { computed, ref } from "vue";
import { defineComponent } from 'vue'
export default defineComponent ({
    setup() {
        const todo = ref<ITodoInterface|undefined>(undefined);
        const todos = ref<ITodoInterface[]>([]);
        let id = 0;
        const numberOfCompletedTodos = computed(
            () => todos.value.filter((todo) => todo.completed).length
        );
        function addTodoItem() {
            todos.value.push(todo.value);
            todo.value = undefined;
            id++;
        }
        function removeTodoItem(index) {
            todos.value.splice(index, 1);
        }
</script>

Answer 5

Answer №3

While grappling with a similar challenge in my Vue.js project that involved a reactive store, I encountered a snag. Merely incorporating an interface did not do the trick. However, explicitly designating a type using [] as Banana[] turned out to be the key solution.

interface Banana {
  description: string;
}
interface BananaStore {
  bananas: Banana[];
}
export const bananaStore: BananaStore = reactive({
  bananas: [] as Banana[]
})

Hopefully, this insight proves beneficial to your situation. Remember to relish the process. Best of luck!

Answer 6

While grappling with a similar challenge in my Vue.js project that involved a reactive store, I encountered a snag. Merely incorporating an interface did not do the trick. However, explicitly designating a type using [] as Banana[] turned out to be the key solution.

interface Banana {
  description: string;
}
interface BananaStore {
  bananas: Banana[];
}
export const bananaStore: BananaStore = reactive({
  bananas: [] as Banana[]
})

Hopefully, this insight proves beneficial to your situation. Remember to relish the process. Best of luck!

Solving the 'never' type issue in Vue3 and TypeScript for an empty array reference

Answer №1

Answer №2

Answer №3

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