Vue3 calculation Properties
Calculation attribute keywords: computed .
Computational attributes are useful when dealing with some complex logic.
Take a look at the following example of reversing a string:
Example 1
<divid="app">{{ message.split('').reverse().join('') }}</div>
In example 1, the template becomes very complex and not easy to understand.
Next, let’s take a look at an example that uses calculated properties:
Example 2
<!DOCTYPEhtml><html><head><metacharset="utf-8"><title>Vue Test Example -
Rookie Tutorial(runoob.com)</title><scriptsrc="https://unpkg.com/vue@next"></script></head><body><divid="app"><p>Original String:
{{ message }}</p><p>Invert string after calculation: {{ reversedMessage
}}</p></div><script>const app = { data() { return { message: 'RUNOOB!!'
} }, computed: { // Calculating attributes getter reversedMessage: function () { //
\`this\` Point to vm instance return this.message.split('').reverse().join('') }
} } Vue.createApp(app).mount('#app')</script>
A calculation property is declared in example 2 reversedMessage .
The function provided will be used as a property vm.reversedMessage of getter .
vm.reversedMessage depend on vm.message in vm.message when there is a change vm.reversedMessage will also be updated.
Computed vs methods
We can use methods to replace computed both of them are the same in effect, but computed is based on its dependency cache and will only be re-valued when the dependency changes. And use methods when re-rendering, the function is always called again to execute
Example 3
methods:{reversedMessage2:function(){returnthis.message.split('').reverse().join('')}}
It can be said to use computed performance will be better, but if you don’t want caching, you can use the methods property.
Computed setter
computed property defaults to only getter but you can also provide one when needed setter :
Example 4
varvm=newVue({el:'#app',data:{name:'Google',url:'http://www.google.com'},computed:{site:{//getterget:function(){returnthis.name+''+this.url},//setterset:function(newValue){varnames=newValue.split('')this.name=names[0]this.url=names[names.length-1]}}}})//call
setter， vm.name and vm.url will also be updated accordingly with vm. site='Rookie Tutorial'
http://www.runoob.com';document.write('name:'+vm.name);document.write('<br>');document.write('url:'+vm.url);
Judging from the running results of the instance, when running vm.site = ‘rookie tutorial http://www.runoob.com’; setter will be called. vm.name and vm.url will also be updated accordingly.
