Return value from function parameter in Javascript

Question

I'm trying to use the fingerprintjs2 javascript library, to get browser fingerprints.

The following code works ok:

new Fingerprint2().get(function (result) {
    var output = result;
    document.write(output);
});

However, I would like to set a variable outside of this block, to be used later e.g.:

var output;

new Fingerprint2().get(function (result) {
    output = result;
});

document.write(output);

but in this case I get the output:

undefined

I'm guessing this is related to scope, so is there any way to set the variable in the outer scope, or do I need to put all following code inside this function call?

I've read other questions about getting the value of nested functions, but none seem to work in this case.

Answer 1

this will not work because you are printing the output before the asynchronous get has returned.

try this:

var output;

var callbackFunction = function(result) {
output = result;
document.write(output);
//do whatever you want to do with output inside this function or call another function inside this function. 
}

new Fingerprint2().get(function (result) {
   // you don't know when this will return because its async so you have to code what to do with the variable after it returns;
   callbackFunction(result);
});

Answer 2

it is not the way u should do it. i"m writeing the code using ES6.

let Fingerprint2Obj = new Fingerprint2().get(function (result) {
    let obj = {
     output: result
    }
    return obj;
});

you can't call the var outside the function, instand if you send it out via object or string. document.write(Fingerprint2Obj.output);