Accessing props in vue component data function

问题

I am passing a props to a component:

<template>
   {{messageId}}
   // other html code
</template>

<script>
   export default {
      props: ['messageId'],
      data: function(){
         var theData={
            // below line gives ReferenceError messageId is not defined
            somevar: messageId,
            // other object attributes
         }
      }
   }
</script>

In above code, I have commented the line that gives the error. If I remove that line, it works as normal and template renders properly (and I can see the expected value of {{messageId}} as well). Hence the logic to pass data is correct.

It seems that the way to access the messageId in data() is wrong. So how do I access the props messageId in data?

回答1:

From the data() method, you can reference the component's properties using this.

So in your case:

data: function() {
  var theData = {
    somevar: this.messageId,
    // other object attributes
  }

  return theData;
}

回答2:

Note that this does not work if you are using an arrow function for assigning your data:

data: () => ({
  somevar: this.messageId // undefined
}),

Because this will not point to the component. Instead, use a plain function:

data: function() {
  return { somevar: this.messageId }
},

or using ES6 object method shorthand as Siva Tumma suggested:

data() {
    return { somevar: this.messageId }
}

回答3:

To assign a data property equal to a props, you can use watcher, as following:

<script>
   export default {
      props: ['messageId'],
      data: function(){
         var theData={
            somevar: "",
            // other object attributes
         }
      },
      watch: {
        messageId: function(newVal) { 
           this.somevar = newVal
        }
      }
   }

回答4:

<template>
   {{messaged}}
   // other HTML code
</template>

<script>
   export default {
      props: ['messaged'],
      data: function(){
         return () {
           some_var: this.messaged
         }
      },
      methods: {
      post_order: function () {
        console.log({
          some_var: this.some_var.id
        })
      }
    }

   }
</script>

来源：https://stackoverflow.com/questions/42722433/accessing-props-in-vue-component-data-function

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