How do I return the response/result from a function foo that makes an asynchronous request?
I am trying to return the value from the callback, as well as assigning the result to a local variable inside the function and returning that one, but none of those ways actually return the response — they all return undefined or whatever the initial value of the variable result is.
Example of an asynchronous function that accepts a callback (using jQuery's ajax function):
function foo() {
var result;
$.ajax({
url: '...',
success: function(response) {
result = response;
// return response; // <- I tried that one as well
}
});
return result; // It always returns `undefined`
}
Example using Node.js:
function foo() {
var result;
fs.readFile("path/to/file", function(err, data) {
result = data;
// return data; // <- I tried that one as well
});
return result; // It always returns `undefined`
}
Example using the then block of a promise:
function foo() {
var result;
fetch(url).then(function(response) {
result = response;
// return response; // <- I tried that one as well
});
return result; // It always returns `undefined`
}