Js.ajax pros and cons, work flow

1, the advantages of Ajax

Ajax to bring us the benefits of all of you are basically deep experience, here I only briefly say a few points:

1, the biggest point is that the page does not refresh, in the page and the server to communicate with the user experience is very good.

2, using the asynchronous way to communicate with the server, do not need to interrupt the user's operation, with more rapid response.

3, can transfer the work of some previous server to the client, take advantage of the client idle ability to handle, reduce the burden of server and bandwidth, save space and broadband rental cost. and reduce the burden on the server, the principle of Ajax is "on-demand data", can minimize redundancy requests, and response to the burden on the server.

4, based on standardized and widely supported technology, do not need to download plug-ins or small programs.

2, the shortcomings of Ajax

Let me focus on the drawbacks of Ajax, because most of the things we pay attention to are the benefits of Ajax, such as the improvement of the user experience. And the shortcomings of Ajax have been neglected.

The drawbacks of Ajax described below are inherently generated.

1, Ajax killed the back button, that is, the browser fallback mechanism of destruction. The Back button is an important feature of a standard web site, but it does not work well with JS. This is a serious problem with Ajax, because users often want to be able to undo the previous operation by going backwards. So is there any way to do this question? The answer is yes, using Gmail know, Gmail under the Ajax technology to solve the problem, in Gmail can be back, but it does not change the mechanism of Ajax, it is only a relatively stupid but effective way, that is, the user click the Back button to access the history To reproduce the changes on the page by creating or using a hidden iframe. (for example, when a user clicks back in Google Maps, it searches in a hidden iframe and then reflects the search results on an AJAX element to restore the application state to its current state.) ）

However, although this problem can be solved, but the development cost of it is very high, and the AJAX framework required by the rapid development is a divergence. This is a very serious problem caused by Ajax.

2, security issues

Technology also poses new security threats to IT companies, and Ajax technology is just like building a direct channel to enterprise data. This allows developers to inadvertently expose more data and server logic than ever before. The logic of Ajax can be hidden from the client's security scanning technology, allowing hackers to create new attacks from remote servers. And Ajax also makes it difficult to avoid some known security weaknesses, such as cross-site footstep attacks, SQL injection attacks, and credentials-based security vulnerabilities.

3, the support of the search engine is weaker.

4. The abnormal mechanism of the program is destroyed. At least for now, these Ajax frameworks, like Ajax.dll,ajaxpro.dll, can disrupt the program's exception mechanism. On this issue, I have encountered in the development process, but looked at the Internet almost no relevant introduction. Then I did a test by myself, using Ajax and the traditional form submission mode to delete a piece of data ... It has brought us a lot of difficulties in debugging.

5, in addition, like some other aspects of the problem, such as violating the URL and resource positioning of the original intention. For example, I give you a URL address, if you use Ajax technology, perhaps you see below the URL address and what I see under this URL is different. This is contrary to the original intention of resource positioning.

6, some handheld devices (such as mobile phones, PDAs, etc.) are not very good to support Ajax, for example, we open the browser on the mobile phone using AJAX technology site, it is currently not supported, of course, this problem and we do not have much to do with.

3. What is the workflow of Ajax?

1. Client-generated JS events
2. Create a XMLHttpRequest Object
3. Configure the XMLHttpRequest
4. Sending asynchronous requests through the AJAX engine
5. Server-side receives requests and processes requests, returning HTML or XML content
6.XML calls a callback () to process the response back to the content
7. Page Local Refresh

4. Ajax Principles and XMLHttpRequest objects

The principle of Ajax is simply to send an asynchronous request to the server via the XMLHttpRequest object, get the data from the server, and then use JavaScript to manipulate the DOM and update the page. One of the most critical steps is getting the request data from the server. To understand this process and principle, we must have some knowledge of xmlhttprequest.

XMLHttpRequest is the core mechanism of Ajax, which was first introduced in IE5 and is a technique that supports asynchronous requests. Simply put, JavaScript can request and process responses to the server in a timely manner without blocking the user. Achieve a no-refresh effect.

Js.ajax pros and cons, work flow