[Vuejs]-Vue – Cannot set property of undefined in response

It’s because you are not binding this in the callback of your http call. You could use an arrow function for example to solve it.

from

 .then(function(res) { 
    console.log(res.data.address); // This returns the address
    alert(res.data.address);
    this.address=res.data.address;
 })

to

 .then((res) => { 
    console.log(res.data.address); // This returns the address
    alert(res.data.address);
    this.address=res.data.address;
 })