It appears there may be some confusion regarding how JavaScript functions operate:
Often it is mistakenly believed that a function initiating an AJAX call should not return until the results are received. The misconception lies in thinking that the AJAX function runs separately in an asynchronous thread.
This notion contains two inaccuracies:
- The belief that a function making an AJAX request must wait for the response before returning.
- The misunderstanding that the AJAX function operates in its own independent asynchronous thread.
Both claims are incorrect, and here's why:
When a function triggers an ajax call, its sole purpose is to send that call – the function returns once the request is dispatched. However, what transpires with the request and how it gets handled upon receiving a response is not within the function's scope. Consider this scenario:
function sendInfo(info)
{
var loader = $('#loader');
$.ajax({
url: 'your/url',
data: info,
type: 'post',
success: function(response)
{
loader.hide();
}
});
loader.show();
}
In this code snippet, the function $.ajax executes the request. If this operation were blocking, the loader display wouldn't be possible. After sending the request, the function concludes, and the success callback initiates upon receiving a response to handle. This callback manages the loader by hiding it again. Responsive and dynamic websites rely on non-blocking AJAX calls which allow for features like autocomplete searches or real-time updates.
The assertion that AJAX functions run in separate threads is inaccurate. AJAX represents a type of request, while the functions you mention refer to either request initiation functions (which do not operate in separate threads) or event callbacks/handlers. These also do not execute in distinct threads.
JavaScript remains single-threaded despite having an event loop. Each event prompts JS to check for linked handlers; if present, these handlers will execute one at a time. During handler execution, no other code can run.
To address your inquiry about returning from such functions: functions inherently return something. If you seek to assign their return value to a variable, direct assignment isn't feasible:
//without jQuery:
var returnVal = xhr.send();
This action does not yield the success (onreadystatechange) handler value because this event occurs multiple times! Alternatively, consider utilizing closure variables, the module pattern, or global variables. Separate threading would result in scope issues, hinder global variable access, and impede DOM manipulation. Instead, opt for approaches like this:
var infoModule = (function()
{
var loader = $('#loader'),
module = {response: undefined};
module.sendInfo = function(info)
{
$.ajax({
url: 'your/url',
data: info,
type: 'post',
success: function(response)
{
loader.hide();
module.response = response;
}
});
loader.show();
};
return module;
}());
With this setup, conduct actions like:
infoModule.sendInfo({data: 'foo'});
Upon completion of the request, assess the response as follows:
infoModule.response;