VueJS data property returns undefined in mounted function

问题

I'm about an hour removed from starting to learn VueJS. I've made a get request using Axios which returns some data as expected, but I cannot access the app's data properties in the mounted function to assign the results of the request. The console log to this.productList returns undefined. Can anyone point me in the right direction?

new Vue({
el: '#products',
data: function(){
    return{
        test: 'Hello',
        productList: null
    }
},
mounted: function(){
    axios.get('https://api.coindesk.com/v1/bpi/currentprice.json').then(function(response){
        console.log(response.data);
        console.log(this.productList)
    }).catch(function(error){
        console.log(error);
    })
}

})

回答1:

Because in that function, this doesn't refer to your vue instance. It has another meaning.

You can make a temporary variable to hold the value of this in the outer function, like this:

mounted: function() {

  let $vm = this;

  axios.get('https://api.coindesk.com/v1/bpi/currentprice.json').then(function(response) {
    console.log(response.data);
    console.log($vm.productList)
  }).catch(function(error) {
    console.log(error);
  })
}

Or you can use the nicer arrow functions:

mounted: function() {

  axios.get('https://api.coindesk.com/v1/bpi/currentprice.json').then((response) => {
    console.log(response.data);
    console.log(this.productList)
  }).catch(function(error) {
    console.log(error);
  })
}

来源：https://stackoverflow.com/questions/51929737/vuejs-data-property-returns-undefined-in-mounted-function