Why does vfor need to add key in vue?

In Vue.js, v-for list items require a unique key attribute to track identification, optimize performance when data changes, and correctly move elements across lists. By setting a unique key, such as the ID or name of a list item, Vue can efficiently update the virtual DOM and avoid unnecessary re-rendering.

Why should we add Key to v-for in Vue

In Vue.js, when using v-for When the directive renders a list, it is usually necessary to add a unique key attribute to each list item. Here are instructions on how and why you need to add a key:

Why do you need a Key?

• Tracking identification: Key allows Vue to track individual elements in the list, thereby efficiently updating the virtual DOM when the data is updated.
• Optimization when data changes: If there is no key, Vue will use the index of the list item as the key by default. When the order of list items changes (for example, items are added or removed), the index changes, causing Vue to re-render all items, which can reduce performance.
• Move elements across lists: Using keys, Vue can track the movement of elements through the list and correctly update the virtual DOM even if their order changes.

How to add Key?

Key can be a string, number, or boolean as long as it is unique in the list. Common practice is to set the key in a unique property of the list item (for example, ID or name). For example:

<code class="html"><ul>
  <li v-for="item in items" :key="item.id">{{ item.name }}</li>
</ul></code>

Other notes:

• Uniqueness is crucial: The key of each list item must be unique , otherwise Vue will not be able to track the element correctly.
• Data structures: The most efficient way to use key is in a data structure where the list items have unique identifiers (for example, an array object).
• Performance impact: Adding key will increase the cost of initial rendering, but it can improve overall performance when the list is updated frequently.

By adding keys to Vue's v-for list items, you can help Vue track elements efficiently, thereby improving performance when data changes and ensuring that the virtual DOM is updated correctly.

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