The key to using v-for to render a list in Vue is to master the basic usage, the importance of binding keys, and precautions. 1. v-for can traverse arrays or objects to render DOM nodes, such as
- {{ item.name }}
It is very common to use v-for to render lists in Vue, which can help us quickly render data from arrays or objects onto pages. The key is to understand its basic usage, the importance of binding keys, and some common notes.
Basic usage: How to render a list with v-for
v-for directive can traverse an array or object and generate the corresponding DOM node for each element. The most commonly used scenario is to render a <ul></ul> or <ol></ol> list.
For example:
<ul>
<li v-for="item in items" :key="item.id">
{{ item.name }}
</li>
</ul> Here items are an array, and item is the element of the current loop. You can also alias each loop item, such as adding an index:
<li v-for="(item, index) in items" :key="item.id">
{{ index 1 }} item: {{ item.name }}
</li>This allows you to access the data and its location in the array at the same time.
Key attributes are very important and cannot be omitted
When using v-for , you must use it with :key , and the value of the key is preferably a unique identifier (such as ID), rather than an array index.
Why? Because Vue will reuse existing nodes as much as possible when updating the virtual DOM. If you do not provide a stable key, Vue may incorrectly reuse component state or DOM elements, causing display exceptions or performance issues.
for example:
- ? Recommended writing method:
:key="item.id" - ? Not recommended writing method:
:key="index"
Especially when used in combination with components, key is more critical, which determines whether Vue wants to recreate the component.
Some details in practical applications
The situation of traversing the object
In addition to arrays, v-for can also be used for objects. The default parameter order is (value, key, index) :
<div v-for="(value, key, index) in user" :key="key">
{{ index 1 }}. {{ key }}: {{ value }}
</div> Assuming user = { name: 'Tom', age: 25 } , the above code will output:
1. name: Tom 2. age: 25
Notes on array change
Vue responsively processes the operation of the array, but not all methods trigger view updates. The following method is the "mutation method", which changes the original array and triggers an update:
- push()
- pop()
- shift()
- unshift()
- splice()
- sort()
- reverse()
However, methods such as filter() , map() , and slice() that do not modify the original array need to be reassigned to trigger an update:
this.items = this.items.filter(item => item.isActive)
Using v-for on template
If you don't want to wrap extra tags, you can use v-for on the <template> tag, which won't be rendered to the actual DOM element:
<template v-for="item in items" :key="item.id">
<li>{{ item.name }}</li>
</template>This is very useful when you need to loop multiple elements and don't want to add an extra layer of container.
Basically that's it. By mastering the usage of v-for , you can easily meet most list rendering needs.
The above is the detailed content of Rendering Lists with Vue v-for Directive. For more information, please follow other related articles on the PHP Chinese website!
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