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Implementing Incremental Data Fetching in Vue.js with TypeScript

Modern web applications often require fetching data dynamically as users interact with the application. Simply fetching all data upfront can lead to slow initial loads and wasted resources. This challenge focuses on implementing an incremental data fetching strategy in a Vue.js application using TypeScript. You will build a component that fetches data in stages, allowing users to see content progressively and only fetching what's immediately needed.

Problem Description

Your task is to create a Vue.js component that demonstrates incremental data fetching. This component will simulate fetching a list of items, and then for each item, it will fetch additional details only when that item is explicitly requested (e.g., by hovering or clicking on it). This approach optimizes performance by deferring the fetching of less critical data until it's actually required by the user.

Key Requirements:

  1. Initial Fetch: The component should fetch a primary list of "items" when it's mounted. Each item in this initial list will have a basic identifier (e.g., id and name).
  2. Incremental Fetch: When a user interacts with an individual item (e.g., hovers over it), the component should trigger a secondary fetch for more detailed information about that specific item. This detailed information should be stored and associated with the item.
  3. State Management: The component should manage the state of both the initial list and the fetched details for each item. This includes handling loading states for both the initial list and individual item details.
  4. TypeScript Integration: The entire solution must be implemented using TypeScript, ensuring strong typing for data structures and component props/state.
  5. Vue 3 Composition API: Utilize Vue 3's Composition API for managing component logic, state, and lifecycle hooks.

Expected Behavior:

  • Upon component mount, a loading indicator should be displayed.
  • Once the initial list of items is fetched, the items should be rendered, and the loading indicator should disappear.
  • When a user interacts with an item, a subtle loading indicator should appear next to that item, and its details should be fetched.
  • Once the details for an item are fetched, they should be displayed alongside the item's basic information, and the item-specific loading indicator should disappear.
  • If the user interacts with an item for which details have already been fetched, the details should be displayed immediately without re-fetching.

Edge Cases to Consider:

  • Network Errors: Handle potential errors during both the initial fetch and the incremental fetches gracefully. Display user-friendly error messages.
  • Rapid Interactions: Consider how the component should behave if a user rapidly hovers over multiple items. Avoid unnecessary duplicate fetches.

Examples

Example 1: Initial Load and First Item Detail Fetch

Input (Simulated API Response for Initial List):

[
  { "id": 1, "name": "Product A" },
  { "id": 2, "name": "Product B" },
  { "id": 3, "name": "Product C" }
]

Input (Simulated API Response for Product A Details, triggered by interaction):

{ "id": 1, "description": "A detailed description for Product A.", "price": 19.99 }

Component State (Initial):

interface Item {
  id: number;
  name: string;
}

interface ItemDetails {
  description: string;
  price: number;
}

const items: Item[] = [];
const itemDetails: Map<number, ItemDetails> = new Map();
const isLoadingInitial: boolean = true;
const isLoadingItemDetails: Map<number, boolean> = new Map();

Component State (After Initial Fetch):

const items: Item[] = [
  { id: 1, name: "Product A" },
  { id: 2, name: "Product B" },
  { id: 3, name: "Product C" }
];
const itemDetails: Map<number, ItemDetails> = new Map();
const isLoadingInitial: boolean = false;
const isLoadingItemDetails: Map<number, boolean> = new Map(); // all false initially

Component State (After Product A Details Fetch):

const items: Item[] = [
  { id: 1, name: "Product A" },
  { id: 2, name: "Product B" },
  { id: 3, name: "Product C" }
];
const itemDetails: Map<number, ItemDetails> = new Map([
  [1, { description: "A detailed description for Product A.", price: 19.99 }]
]);
const isLoadingInitial: boolean = false;
const isLoadingItemDetails: Map<number, boolean> = new Map([
  [1, false],
  [2, false],
  [3, false]
]);

Explanation: The component first fetches the basic list of products. Upon hovering over "Product A", a request is made to fetch its details. Once those details are received, they are stored and displayed alongside "Product A".

Example 2: Fetching details for another item and displaying cached data

Input (Simulated API Response for Product B Details, triggered by interaction):

{ "id": 2, "description": "The comprehensive breakdown of Product B.", "price": 29.50 }

Component State (Before Product B Detail Fetch):

(Same as after Product A details fetch in Example 1)

Component State (After Product B Details Fetch):

const items: Item[] = [
  { id: 1, name: "Product A" },
  { id: 2, name: "Product B" },
  { id: 3, name: "Product C" }
];
const itemDetails: Map<number, ItemDetails> = new Map([
  [1, { description: "A detailed description for Product A.", price: 19.99 }],
  [2, { description: "The comprehensive breakdown of Product B.", price: 29.50 }]
]);
const isLoadingInitial: boolean = false;
const isLoadingItemDetails: Map<number, boolean> = new Map([
  [1, false],
  [2, false],
  [3, false]
]);

Explanation: After fetching details for "Product A", the user then interacts with "Product B". Its details are fetched and stored. If the user were to interact with "Product A" again, its details would be displayed instantly from the itemDetails map.

Constraints

  • The simulated API calls should take between 500ms and 2000ms to respond to mimic real-world network latency.
  • The initial fetch should be for a list of at least 5 items.
  • Each item detail fetch should be for a distinct set of data.
  • Your component should be a functional component using the Composition API.
  • All data models and component logic should be typed using TypeScript.
  • Avoid using any third-party state management libraries (e.g., Pinia, Vuex). Manage state within the component.

Notes

  • You will need to simulate API calls. You can achieve this using setTimeout and Promise to mimic asynchronous network requests.
  • Consider how to represent the loading state for individual items. A Map where keys are item IDs and values are booleans (true if loading) is a good approach.
  • Think about the event that triggers the detail fetch. A simple hover effect is a good starting point, but you can explore other interactions.
  • Ensure your TypeScript interfaces accurately reflect the expected data structures.
  • The goal is to demonstrate the pattern of incremental fetching and state management within a Vue component. The specific UI presentation (e.g., how details are shown) is secondary to the underlying data fetching and state logic.
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