javascript - Executing async functions with a callback? -

I am a little confused about how to create and use callback functions while working with async requests. All examples are online as an async function. Want to use the SetTimeout function to copy, but I want an example which uses only a real world API.

I have an async function that takes a zip code and returns a JSON like this:

  {"post code": "90210", "country": "United States": "State": "America", "Location": [["Location name": "Beverly Hills", "Longitude": "-118.4065", "State": "California", "State abbreviation Name ":" CA "," Latitude ":" 34.0901 "}}}  

These functions go to the Async function API and give up JSON.

Just takes JSON in the sync function and returns the city's string to the upper seas

  // async Function var ReturnLocationInfoByZip = function (zip) {var client = new XMLHttpRequest (); Miscellaneous feedback; Client.open ("GET", "http: // api .zippopotam.us / us / "+ zip, true); Client.onreadystatechange = function () {if (client.readyState == 4) {response = client.responseText; return response;};}; client.send () ;}} // Sync Function var city toupper onCase = function (reaction object) {var city = response object.place [0] ["name of place"]; return city. Uppercase ();};  

The following code flow does not work because I call I'm not using back. What would be the most obvious way of executing these tasks, so that I can get the desired console log in the name of the city in all uppercase?

  // obviously not var zip = "94043"; Var responseobox = return location: Infobjip (zip); // Here I want to console the upper case city name to var cityInUpperCase = cityToUpperCase (responseObject); Console.log (cityInUpperCase); Edit: Bah, it seems that the answer may be:  
 I still would be interested in knowing how to do this with this example Though.   
 
 
 You have to pass the sync function ( cityToUpperCase ) as a parameter Async function ( returnLocationInfoByZip ) will apply when it is called  onreadystatechange : 
 
  var returnLocationInfoByZip = function (zip, callback) {. .. client.onreadystatechange = function () {if (client.readyState == 4) {response = client.responseText; Callback (json.parse); }; }; ...} var cityToUpperCase = functionObject {...}; ... Back to location location InfoByZip (zip, function (feedback object) {console.log (cityToUpperCase (responseObject))});