title: VueJS data property returns undefined in mounted function
body: <p>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 <code>this.productList</code> returns <code>undefined</code>. Can anyone point me in the right direction?</p>
  <pre><code>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);
          })
      }
      
  })
  </code></pre>