How to use Vue.js computed properties with listeners
This time I will show you how to use Vue.js calculated properties and listeners. What are the precautions for using Vue.js calculated properties and listeners. The following is a practical case. Let’s take a look. take a look.
1. Overview
Calculated properties
The expression in the template is very convenient, but They were originally designed for simple calculations. Putting too much logic into a template can make it overweight and difficult to maintain. For example:
<p id="example">
{{ message.split('').reverse().join('') }}
</p>Here, the template is no longer simple declarative logic. You have to watch for a while to realize that here you want to display the flippedString of the variable message. It becomes more difficult to deal with when you want to reference the flipped string here multiple times in the template.
So, for any complex logic, you should use computed properties.
Basic example
<p id="example">
<p>Original message: "{{ message }}"</p>
<p>Computed reversed message: "{{ reversedMessage }}"</p>
</p>
var vm = new Vue({
el: '#example',
data: {
message: 'Hello'
},
computed: {
// 计算属性的 getter
reversedMessage: function () {
// `this` 指向 vm 实例
return this.message.split('').reverse().join('')
}
}
})Result:
console.log(vm.reversedMessage) // => 'olleH' vm.message = 'Goodbye' console.log(vm.reversedMessage) // => 'eybdooG'
2. Computed property cache vs method
You may have noticed that we can achieve the same effect by calling methods in expressions<p>Reversed message: "{{ reversedMessage() }}"</p>
// 在组件中
methods: {
reversedMessage: function () {
return this.message.split('').reverse().join('')
}
}computed: {
now: function () {
return Date.now()
}
}3. Computed properties vs listening properties
Vue provides a more general way to observe and respond to data on Vue instances Changed: Listening properties. When you have some data that needs to change asother data changes, it's easy to abuse watches - especially if you've used AngularJS before. However, it is often better to use computed properties instead of imperative watch callbacks.
Think about this example<p id="demo">{{ fullName }}</p>
var vm = new Vue({
el: '#demo',
data: {
firstName: 'Foo',
lastName: 'Bar',
fullName: 'Foo Bar'
},
watch: {
firstName: function (val) {
this.fullName = val + ' ' + this.lastName
},
lastName: function (val) {
this.fullName = this.firstName + ' ' + val
}
}
})var vm = new Vue({
el: '#demo',
data: {
firstName: 'Foo',
lastName: 'Bar'
},
computed: {
fullName: function () {
return this.firstName + ' ' + this.lastName
}
}
})4. Computed property setters
Computed properties only have getters by default, but you can also provide a setter when needed// ...
computed: {
fullName: {
// getter
get: function () {
return this.firstName + ' ' + this.lastName
},
// setter
set: function (newValue) {
var names = newValue.split(' ')
this.firstName = names[0]
this.lastName = names[names.length - 1]
}
}
}
// ...现在再运行 vm.fullName = 'John Doe' 时，setter 会被调用，vm.firstName 和 vm.lastName 也会相应地被更新。
五、侦听器
虽然计算属性在大多数情况下更合适，但有时也需要一个自定义的侦听器。这就是为什么 Vue 通过 watch 选项提供了一个更通用的方法，来响应数据的变化。当需要在数据变化时执行异步或开销较大的操作时，这个方式是最有用的。
例如：
<p id="watch-example">
<p>
Ask a yes/no question:
<input v-model="question">
</p>
<p>{{ answer }}</p>
</p>
<!-- 因为 AJAX 库和通用工具的生态已经相当丰富，Vue 核心代码没有重复 -->
<!-- 提供这些功能以保持精简。这也可以让你自由选择自己更熟悉的工具。 -->
<script src="https://cdn.jsdelivr.net/npm/axios@0.12.0/dist/axios.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/lodash@4.13.1/lodash.min.js"></script>
<script>
var watchExampleVM = new Vue({
el: '#watch-example',
data: {
question: '',
answer: 'I cannot give you an answer until you ask a question!'
},
watch: {
// 如果 `question` 发生改变，这个函数就会运行
question: function (newQuestion, oldQuestion) {
this.answer = 'Waiting for you to stop typing...'
this.getAnswer()
}
},
methods: {
// `_.debounce` 是一个通过 Lodash 限制操作频率的函数。
// 在这个例子中，我们希望限制访问 yesno.wtf/api 的频率
// AJAX 请求直到用户输入完毕才会发出。想要了解更多关于
// `_.debounce` 函数 (及其近亲 `_.throttle`) 的知识，
// 请参考：https://lodash.com/docs#debounce
getAnswer: _.debounce(
function () {
if (this.question.indexOf('?') === -1) {
this.answer = 'Questions usually contain a question mark. ;-)'
return
}
this.answer = 'Thinking...'
var vm = this
axios.get('https://yesno.wtf/api')
.then(function (response) {
vm.answer = _.capitalize(response.data.answer)
})
.catch(function (error) {
vm.answer = 'Error! Could not reach the API. ' + error
})
},
// 这是我们为判定用户停止输入等待的毫秒数
500
)
}
})
</script>结果：当没有输入？号，那么显示如下：
当有?时候会输出“yes”或者“no”
具体案例效果地址：侦听器
在这个示例中，使用 watch 选项允许我们执行异步操作 (访问一个 API)，限制我们执行该操作的频率，并在我们得到最终结果前，设置中间状态。这些都是计算属性无法做到的。
相信看了本文案例你已经掌握了方法，更多精彩请关注php中文网其它相关文章！
推荐阅读：
The above is the detailed content of How to use Vue.js computed properties with listeners. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
How to use mdf and mds files
Feb 19, 2024 pm 05:36 PM
How to use mdf files and mds files With the continuous advancement of computer technology, we can store and share data in a variety of ways. In the field of digital media, we often encounter some special file formats. In this article, we will discuss a common file format - mdf and mds files, and introduce how to use them. First, we need to understand the meaning of mdf files and mds files. mdf is the extension of the CD/DVD image file, and the mds file is the metadata file of the mdf file.
What software is crystaldiskmark? -How to use crystaldiskmark?
Mar 18, 2024 pm 02:58 PM
CrystalDiskMark is a small HDD benchmark tool for hard drives that quickly measures sequential and random read/write speeds. Next, let the editor introduce CrystalDiskMark to you and how to use crystaldiskmark~ 1. Introduction to CrystalDiskMark CrystalDiskMark is a widely used disk performance testing tool used to evaluate the read and write speed and performance of mechanical hard drives and solid-state drives (SSD). Random I/O performance. It is a free Windows application and provides a user-friendly interface and various test modes to evaluate different aspects of hard drive performance and is widely used in hardware reviews
How to download foobar2000? -How to use foobar2000
Mar 18, 2024 am 10:58 AM
foobar2000 is a software that can listen to music resources at any time. It brings you all kinds of music with lossless sound quality. The enhanced version of the music player allows you to get a more comprehensive and comfortable music experience. Its design concept is to play the advanced audio on the computer The device is transplanted to mobile phones to provide a more convenient and efficient music playback experience. The interface design is simple, clear and easy to use. It adopts a minimalist design style without too many decorations and cumbersome operations to get started quickly. It also supports a variety of skins and Theme, personalize settings according to your own preferences, and create an exclusive music player that supports the playback of multiple audio formats. It also supports the audio gain function to adjust the volume according to your own hearing conditions to avoid hearing damage caused by excessive volume. Next, let me help you
How to use NetEase Mailbox Master
Mar 27, 2024 pm 05:32 PM
NetEase Mailbox, as an email address widely used by Chinese netizens, has always won the trust of users with its stable and efficient services. NetEase Mailbox Master is an email software specially created for mobile phone users. It greatly simplifies the process of sending and receiving emails and makes our email processing more convenient. So how to use NetEase Mailbox Master, and what specific functions it has. Below, the editor of this site will give you a detailed introduction, hoping to help you! First, you can search and download the NetEase Mailbox Master app in the mobile app store. Search for "NetEase Mailbox Master" in App Store or Baidu Mobile Assistant, and then follow the prompts to install it. After the download and installation is completed, we open the NetEase email account and log in. The login interface is as shown below
How to use Baidu Netdisk app
Mar 27, 2024 pm 06:46 PM
Cloud storage has become an indispensable part of our daily life and work nowadays. As one of the leading cloud storage services in China, Baidu Netdisk has won the favor of a large number of users with its powerful storage functions, efficient transmission speed and convenient operation experience. And whether you want to back up important files, share information, watch videos online, or listen to music, Baidu Cloud Disk can meet your needs. However, many users may not understand the specific use method of Baidu Netdisk app, so this tutorial will introduce in detail how to use Baidu Netdisk app. Users who are still confused can follow this article to learn more. ! How to use Baidu Cloud Network Disk: 1. Installation First, when downloading and installing Baidu Cloud software, please select the custom installation option.
BTCC tutorial: How to bind and use MetaMask wallet on BTCC exchange?
Apr 26, 2024 am 09:40 AM
MetaMask (also called Little Fox Wallet in Chinese) is a free and well-received encryption wallet software. Currently, BTCC supports binding to the MetaMask wallet. After binding, you can use the MetaMask wallet to quickly log in, store value, buy coins, etc., and you can also get 20 USDT trial bonus for the first time binding. In the BTCCMetaMask wallet tutorial, we will introduce in detail how to register and use MetaMask, and how to bind and use the Little Fox wallet in BTCC. What is MetaMask wallet? With over 30 million users, MetaMask Little Fox Wallet is one of the most popular cryptocurrency wallets today. It is free to use and can be installed on the network as an extension
How to use Xiaoai Speaker How to connect Xiaoai Speaker to mobile phone
Feb 22, 2024 pm 05:19 PM
After long pressing the play button of the speaker, connect to wifi in the software and you can use it. Tutorial Applicable Model: Xiaomi 12 System: EMUI11.0 Version: Xiaoai Classmate 2.4.21 Analysis 1 First find the play button of the speaker, and press and hold to enter the network distribution mode. 2 Log in to your Xiaomi account in the Xiaoai Speaker software on your phone and click to add a new Xiaoai Speaker. 3. After entering the name and password of the wifi, you can call Xiao Ai to use it. Supplement: What functions does Xiaoai Speaker have? 1 Xiaoai Speaker has system functions, social functions, entertainment functions, knowledge functions, life functions, smart home, and training plans. Summary/Notes: The Xiao Ai App must be installed on your mobile phone in advance for easy connection and use.
Teach you how to use the new advanced features of iOS 17.4 'Stolen Device Protection'
Mar 10, 2024 pm 04:34 PM
Apple rolled out the iOS 17.4 update on Tuesday, bringing a slew of new features and fixes to iPhones. The update includes new emojis, and EU users will also be able to download them from other app stores. In addition, the update also strengthens the control of iPhone security and introduces more "Stolen Device Protection" setting options to provide users with more choices and protection. "iOS17.3 introduces the "Stolen Device Protection" function for the first time, adding extra security to users' sensitive information. When the user is away from home and other familiar places, this function requires the user to enter biometric information for the first time, and after one hour You must enter information again to access and change certain data, such as changing your Apple ID password or turning off stolen device protection.
