How to return a value from Javascript callback function?

Question

This question may seem duplicate but unfortunately I couldn't understand other answers.

I'm trying to assign value from callback function to parent variable.

For example

let orientation = null;
orientation = Exif.getData(image, function(){
   return "somevalue";
});

Here how can I assign "somevalue" to orientation?

I believe `Exif.getData` is an asynchronous function, so you will have to `await` it in an `async` function to use it synchronously. — Ace, Jun 22 '19 at 20:53
See also my blog post [JavaScript: How (not) to get a value “out of” a callback](https://felix-kling.de/blog/2019/javascript-callbacks-misconceptions.html). — Felix Kling, Jun 22 '19 at 21:00

score -1 · Answer 1 · answered Jun 22 '19 at 19:56

-1

You can do it the following way:

let orientation = null;
Exif.getData(image, function(){
   orientation = "somevalue";
});
...
if(!orientation) //The callback probably did not run

answered Jun 22 '19 at 19:56

Bruno Tavares

I tried that but returns "True" only. – she hates me Jun 22 '19 at 20:01
Sorry, I was set orientation = Exif.getData but now it return null with this code. – she hates me Jun 22 '19 at 20:04
This appears to be a problem with the exif-js lib. I have been testing it and the callback code does not run. – Bruno Tavares Jun 23 '19 at 18:51

1 Answers1