javascript - ajax asynchronous problem

Excuse me, is the callback function in ajax return data and then execute the code in the function or directly execute the code in the function without waiting for data to be returned?

If it is the second case, how to avoid the trouble caused by asynchronous?

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Excuse me, is the callback function in ajax return data and then execute the code in the function or directly execute the code in the function without waiting for data to be returned?

If it is the second case, how to avoid the trouble caused by asynchronous?

The callback function of success is a function to be executed after the data returns successfully, which means that it will be executed after getting the data.
Other situations include beforeSend (before sending), complete (after the request is completed), error (request error) ) callback

As for the trouble you mentioned caused by asynchronousness, I don’t quite understand it. Can you give me an example?

You must return data and then execute the code in the function = = Execute without returning data = = Isn’t it waiting for an error?

The full name of

ajaxAJAX = Asynchronous JavaScript and XML (asynchronous JavaScript and XML).
To answer your question first, in the case of success, the function will not be executed until data is successfully returned. If there is no return, it will wait for a while. This time is usually the network delay time. You can also set it yourself.

The following is a brief introduction to the ajax of the great jqueryframework.
Usually, I use it like this, in the form of name+value.

<code>$.ajax({name:value, name:value, ... })</code>

• async Boolean value indicating whether the request is processed asynchronously. The default is true. Set to false, you will turn off asynchrony. At this time, one request will cause the interface to be very stuck.

• beforeSend(xhr) Function that runs before sending a request.

• cache Boolean value indicating whether the browser caches the requested page. The default is true.

• complete(xhr,status) Function that runs when the request is completed (called after the request succeeds or fails, that is, after the success and error functions).

• contentType The content type used when sending data to the server. The default is: "application/x-www-form-urlencoded".

• context specifies the "this" value for all AJAX related callback functions.

• data Specifies the data to be sent to the server.

• dataFilter(data,type) Function used to process XMLHttpRequest raw response data.

• dataType The expected data type of the server response.

• error(xhr, status, error) Function to run if the request fails.

• global Boolean value that specifies whether the global AJAX event handler is triggered for the request. The default is true.

• ifModified Boolean value that specifies whether the request will succeed only if the response has changed since the last request. The default is false.

• jsonp rewrites the string of the callback function in a jsonp.

• jsonpCallback specifies the name of the callback function in a jsonp.

• password specifies the password used in HTTP access authentication requests.

• processData Boolean value that specifies whether the data sent through the request is converted to a query string. The default is true.

• scriptCharset specifies the requested character set.

• success(result,status,xhr) Function that runs when the request is successful.

• timeout Set the local request timeout (in milliseconds).

• traditional Boolean value, specifies whether to use the traditional style of parameter serialization.

• type Specifies the type of request (GET or POST).

• url Specifies the URL to send the request. The default is the current page.

• username specifies the username used in HTTP access authentication requests. This can simulate user login, plus password, you know.

• xhr Function used to create XMLHttpRequest objects.

The red part is what I commonly use.

Call back this success function after the interface you requested successfully responds with data, so as long as your server handles it normally, the data returned is the data you want

The answer to the question has been mentioned above, so I won’t repeat it. I just want to ask you about the problems of asynchronousness.