Turn XMLhttpRequest into a function fails: asynchronity or other?

Question

I try to turn an XMLHttpRequest into a function such

var getImageBase64 = function (url) { // code function
    var xhr = new XMLHttpRequest(url); 
    ...          


        

Answer 1

Asynchronous calls in JavaScript (like xhr) can't return values like regular functions. The common pattern used when writing asynchronous functions is this:

function asyncFunc(param1, param2, callback) {
  var result = doSomething();
  callback(result);
}

asyncFunc('foo', 'bar', function(result) {
  // result is what you want
});

So your example translated looks like this:

var getImageBase64 = function (url, callback) {
    var xhr = new XMLHttpRequest(url); 
    ... // code to load file 
    ... // code to convert data to base64
    callback(wanted_result);
}
getImageBase64('http://fiddle.jshell.net/img/logo.png', function(newData) {
  doSomethingWithData($("#hook"), newData);
});