What does as in vue mean?

In Vue.js, as is an optional parameter of the v-for directive, used to specify the attributes that should be used by each element in the loop. This parameter can be used to iterate an array or object into DOM elements. In this article, we’ll take a closer look at what as does and how to use it.

v-forBasic usage

In Vue.js, use the v-for directive to bind an array or object to data The content is looped and rendered into the template. The following is a simple example:

<div id="app">
  <h1>遍历数组：</h1>
  <ul>
    <li v-for="fruit in fruits">{{ fruit }}</li>
  </ul>
  <h1>遍历对象：</h1>
  <ul>
    <li v-for="(value, key) in student">{{ key }}：{{ value }}</li>
  </ul>
</div>

new Vue({
  el: '#app',
  data: {
    fruits: ['apple', 'banana', 'orange'],
    student: {
      name: 'Tom',
      age: 18,
      gender: 'male'
    }
  }
})

In the above code, the v-for instructions are used to traverse arrays and objects respectively. When iterating over the array, we name each element in the array fruit and then use that variable directly when rendering. When iterating over the object, we use parentheses to surround value and key so that we can get the value and key of each property.

as Usage

By default, the syntax of the v-for instruction is as follows: v-for=" item in items". The item here is the variable name we use to refer to the element currently being iterated. To better understand this concept, let's look at the following example:

<div id="app">
  <h1>默认情况下：</h1>
  <ul>
    <li v-for="fruit in fruits">{{ fruit }}</li>
  </ul>
  <h1>使用 as 参数：</h1>
  <ul>
    <li v-for="fruit as f in fruits">{{ f }}</li>
  </ul>
</div>

Unlike the previous example, we now use as# in the v-for directive ## Parameters and a new variable name f. When we use the as parameter, we can also choose a new variable name to reference the currently iterated element in the template. In this example, we could name the iterated element fruit and then use the f variable to reference it in the template.

as This feature provides greater flexibility for looping structures in Vue.js. In some cases, you can make your code more readable and maintainable by giving your loop elements a unique name. Notes on

as

Although the

as feature is very useful, there are some things you need to pay attention to when using it in practice. The following are a few situations that should be noted:

1. Naming convention

Although it is valid to use variable names

as in v-for , but we should avoid using this naming convention in other contexts. The reason is that as is easier to understand as a proprietary prefix to specify a variable name. Therefore, if you use this naming convention elsewhere, it may result in code that is difficult to understand.

2. The use of arrow functions in

as parameters

When writing in Vue.js, especially using TypeScript, sometimes we need to use arrow functions to

as Parameters map to objects. In this case, we should explicitly specify the arrow function as follows:

<div id="app">
  <ul>
    <li v-for="(fruit, index) => ({name: fruit, position: index}) as f">{{ f.name }}: {{ f.position }}</li>
  </ul>
</div>

In the above example, we use the arrow function to combine

name and position Attributes are mapped to a new object. Note that in this example we are using parentheses around the arrow function to let Vue.js know that we are defining a custom mapping rule for the as parameter.

Conclusion

In this article, we introduced an optional parameter

as of the v-for directive in Vue.js, which provides Greater flexibility in specifying variable names for iterated elements. While this feature is very useful, we still need to pay attention to naming conventions and how to map an object to as arguments when using arrow functions.

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