Question
This question already has answers here :
[How do I return the response from an asynchronous call?](/questions/14220321/how-do-i-return-the-response-from-an-asynchronous- call) (41 answers)
Closed 8 years ago.
This question is asked many times in SO. But still I can't get stuff.
I want to get some value from callback. Look at the script below for clarification.
function foo(address){
// google map stuff
geocoder.geocode( { 'address': address}, function(results, status) {
results[0].geometry.location; // I want to return this value
})
}
foo(); //result should be results[0].geometry.location; value
If I try to return that value just getting "undefined". I followed some ideas from SO, but still fails.
Those are:
function foo(address){
var returnvalue;
geocoder.geocode( { 'address': address}, function(results, status) {
returnvalue = results[0].geometry.location;
})
return returnvalue;
}
foo(); //still undefined
Answer
This is impossible as you cannot return from an asynchronous call inside a synchronous method.
In this case you need to pass a callback to foo that will receive the return value
function foo(address, fn){
geocoder.geocode( { 'address': address}, function(results, status) {
fn(results[0].geometry.location);
});
}
foo("address", function(location){
alert(location); // this is where you get the return value
});
The thing is, if an inner function call is asynchronous, then all the functions 'wrapping' this call must also be asynchronous in order to 'return' a response.
If you have a lot of callbacks you might consider taking the plunge and use a promise library like Q.
