Javascript copy object from function

Question

I have problem when copy object from a function in JavaScript.

I have script :

JavaScript

var _img;
fabric.Image.fromURL('phone.png', function(img){
    img.setWidth(320);
    img.setHeight(615);
    img.setLeft(0);
    img.setTop(0);
    canvas.insertAt(img, 0);
    img.set('evented', false);
    _img = Object.assign({}, img);
    console.log(_img);
});

console.log(_img);

the problem is, 2nd console.log result is undefined . I want to copy object from img to _img for reason. How to do that in a proper way ?. Thank you.

Edit : Thank you. I found solution from here : How do I return the response from an asynchronous call? . Now i can get return value from async call, here the code :

function addImage(callback){
  fabric.Image.fromURL('phone.png', function(img){
      callback (img);
  });
}


var _img;
addImage(function(result){
  _img = result; 
  console.log(_img); // result is ok
})
console.log(_img); // result still undefined

But, i still can pass the result to _img object. What should I do ?