How do I get the value in the callback function of a JS asynchronous function? __ Data structure

The Chrome.cookies.get function is asynchronous and, if so, writes:

function GetCookie () {
var result={};
Chrome.cookies.get ({' name ': ' Prouserid ', ' url ':d omain[0]}, function (cookie) {
        Result=cookie;}
    );
return result;

Then the function return value can only be undefined, and the value of the cookie cannot be taken.

Netizens have given a method as follows:

function GetCookie () {
chrome.cookies.get ({' name ': ' Prouserid ', ' url ':d omain[0]}, function (cookie) {
        Donext ( Cookies)

;} function Donext (cookie) {
    console.log (' 123 ');
    Console.log (cookie);
    Console.log (' 456 ');
}

You can get the value normally.

For the characteristics of JS asynchronous function, or to study AH ~ ~ ~