方法vs Vue计算

Vue.js中方法和计算值的主要区别是什么?

在我看来，它们是一样的，是可以互换的。

当前回答

@gleenk需要一个实际的例子来说明方法和计算属性之间的缓存和依赖关系的差异，我将展示一个简单的场景:

app.js

new Vue({
    el: '#vue-app',
    data: {
        a: 0,
        b: 0,
        age: 20
    },
    methods: {
        addToAmethod: function(){
            console.log('addToAmethod');
            return this.a + this.age;
        },
        addToBmethod: function(){
            console.log('addToBmethod');
            return this.b + this.age;
        }
    },
    computed: {
        addToAcomputed: function(){
            console.log('addToAcomputed');
            return this.a + this.age;
        },
        addToBcomputed: function(){
            console.log('addToBcomputed');
            return this.b + this.age;
        }
    }
});

Here we have 2 methods and 2 computed properties that perform the same task. The methods addToAmethod & addToBmethod and the computed properties addToAcomputed & addToBcomputed all add +20 (i.e. the age value) to either a or b. Regarding the methods, they are both called every time an action has been performed on any of the listed properties, even if the dependencies for one specific method have not changed. For the computed properties, the code is executed only when a dependency has changed; for example, one of the specific property values that refers to A or B will trigger addToAcomputed or addToBcomputed, respectively.

方法和计算描述看起来非常相似，但正如@Abdullah Khan已经指定的那样，它们不是一回事!现在让我们尝试添加一些html来一起执行所有内容，看看有什么不同。

方法案例演示

new Vue({ el: '#vue-app', data: { a: 0, b: 0, age: 20 }, methods: { addToAmethod: function(){ console.log('addToAmethod'); return this.a + this.age; }, addToBmethod: function(){ console.log('addToBmethod'); return this.b + this.age; } } }); <!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>VueJS Methods - stackoverflow</title> <link href="style.css" rel="stylesheet" /> <script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.11/vue.min.js"></script> </head> <body> <div id="vue-app"> <h1>Methods</h1> <button v-on:click="a++">Add to A</button> <button v-on:click="b++">Add to B</button> <p>Age + A = {{ addToAmethod() }}</p> <p>Age + B = {{ addToBmethod() }}</p> </div> </body> <script src="app.js"></script> </html>

解释结果

When I click on the button "Add to A", all the methods are called (see the console log screen result above), the addToBmethod() is also executed but I didn't press the "Add to B" button; the property value that refers to B has not changed. The same behaviour comes if we decide to click the button "Add to B", because again both the methods will be called independently of dependency changes. According to this scenario this is bad practice because we are executing the methods every time, even when dependencies have not changed. This is really resource consuming because there is not a cache for property values that have not changed.

Computed属性案例演示

new Vue({ el: '#vue-app', data: { a: 0, b: 0, age: 20 }, computed: { addToAcomputed: function(){ console.log('addToAcomputed'); return this.a + this.age; }, addToBcomputed: function(){ console.log('addToBcomputed'); return this.b + this.age; } } }); <!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>VueJS Computed properties - stackoverflow</title> <link href="style.css" rel="stylesheet" /> <script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.11/vue.min.js"></script> </head> <body> <div id="vue-app"> <h1>Computed Properties</h1> <button v-on:click="a++">Add to A</button> <button v-on:click="b++">Add to B</button> <p>Age + A = {{ addToAcomputed }}</p> <p>Age + B = {{ addToBcomputed }}</p> </div> </body> <script src="app.js"></script> </html>

解释结果

When I click on the button "Add to A", only the computed property addToAcomputed is called because, as we already said, the computed properties are executed only when a dependency has changed. And since I didn't press the button "Add to B" and the age property value for B has not changed, there is no reason to call and execute the computed property addToBcomputed. So, in a certain sense, the computed property is maintaining the "same unchanged" value for the B property like a kind of cache. And in this circumstance this is consider good practice.

2018-01-08 13:33:34

其他回答

下面是这个问题的详细分析。

何时使用方法

对DOM中发生的事件做出反应在组件中发生事情时调用函数。可以从计算属性或观察器调用方法。

何时使用计算属性

您需要从现有数据源组合新数据在模板中使用的变量是由一个或多个数据属性构建的您希望将复杂的、嵌套的属性名称简化为更易于阅读和使用的名称(但在原始属性更改时更新它) 您需要从模板引用一个值。在这种情况下，创建计算属性是最好的，因为它是缓存的。您需要侦听多个数据属性的更改

2019-03-17 16:52:16

计算属性

计算属性也称为计算值。这意味着，它们可以随时更新和更改。此外，它还缓存数据，直到数据发生更改。在实例化Vue时，计算属性将转换为属性。

还有一件事我想分享，你不能在计算属性中传递任何参数，这就是为什么在调用任何计算机属性时不需要括号。

方法

方法与函数相同，以相同的方式工作。此外，除非调用方法，否则方法什么也不做。此外，像所有javascript函数一样，它接受参数，并且每次调用时都会重新计算。之后，它们就不能缓存值了

在方法中调用圆括号，你可以发送一个或多个参数。

2018-07-11 10:59:52

Vue中的计算值和方法非常不同，在大多数情况下肯定是不可互换的。

计算属性

A more appropriate name for a computed value is a computed property. In fact, when the Vue is instantiated, computed properties are converted into a property of the Vue with a getter and sometimes a setter. Basically you can think of a computed value as a derived value that will be automatically updated whenever one of the underlying values used to calculate it is updated. You don't call a computed and it doesn't accept any parameters. You reference a computed property just like you would a data property. Here's the classic example from the documentation:

computed: {
  // a computed getter
  reversedMessage: function () {
    // `this` points to the vm instance
    return this.message.split('').reverse().join('')
  }
}

它在DOM中是这样引用的:

<p>Computed reversed message: "{{ reversedMessage }}"</p>

计算值对于操作Vue上存在的数据非常有价值。每当您想要过滤或转换数据时，通常都会使用计算值来实现此目的。

data:{
    names: ["Bob", "Billy", "Mary", "Jane"]
},
computed:{
    startsWithB(){
        return this.names.filter(n => n.startsWith("B"))
    }
}

<p v-for="name in startsWithB">{{name}}</p>

计算值也会被缓存，以避免重复计算一个没有改变时不需要重新计算的值(例如，因为它可能不在循环中)。

方法

方法只是绑定到Vue实例的函数。它只在显式调用时才会被求值。像所有的javascript函数一样，它接受参数，并且每次被调用时都会被重新求值。方法在同样的情况下也很有用，任何函数都有用。

data:{
    names: ["Bob", "Billy", "Mary", "Jane"]
},
computed:{
    startsWithB(){
        return this.startsWithChar("B")
    },
    startsWithM(){
        return this.startsWithChar("M")
    }
},
methods:{
    startsWithChar(whichChar){
        return this.names.filter(n => n.startsWith(whichChar))
    }
}

Vue的文档非常好，而且易于访问。我推荐它。

2017-06-04 05:05:49

来自文档

..计算属性是基于它们的依赖项缓存的。计算属性只有在其某些依赖项发生更改时才会重新计算。

如果您希望缓存数据，请使用Computed属性，另一方面，如果您不想缓存数据，请使用简单的Method属性。

2017-06-04 13:21:53

在vue 3附带的vue组合API中，可以作为vue 2的插件使用，方法和计算属性是不同的语法:

例子:

计算:

它是一个默认接受getter回调作为参数的函数，并根据其他属性(如ref, reactive或store state)返回一个不可变的ref。

import {computed,ref} from 'vue'

export default{

setup(){
  const count=ref(0);
  
  const doubleCount=computed(()=>count.value*2) 

 return {count,doubleCount} //expose the properties to the template 
 }
}

方法

它们是纯javascript函数，在Vue和vanilla js中以相同的方式表现，它们暴露在模板中并用作事件处理程序，它们不应该用于渲染目的，这可能会导致一些问题，如无限渲染。

import {computed,ref} from 'vue'

export default{

setup(){
  const count=ref(0);
  
  const doubleCount=computed(()=>count.value*2) 
 
  function increment(){
   ref.value++
 }

 return {count,doubleCount,increment} //expose the properties/functions to the template 
 }
}

区别在于:

计算:

它被计算为不可变属性，而不是函数它观察另一个属性并基于该属性返回一个属性。它不能带参数。可以使用watch属性观看它

方法:

用于重构computed/watcher属性或其他函数中的代码用作事件处理程序为了避免呈现问题，不应该在模板中调用它。

2021-03-27 11:23:01

方法vs Vue计算

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