1. What is AJAX and why should we use Ajax (please talk about your understanding of Ajax)
What is ajax:
AJAX is the abbreviation of "Asynchronous JavaScript and XML". It refers to a web development technology for creating interactive web applications.
Ajax includes the following technologies:
Based on web standards (standards-basedpresentation) XHTML CSS representation;
Using DOM (Document ObjectModel ) for dynamic display and interaction;
Use XML and XSLT for data exchange and related operations;
Use XMLHttpRequest for asynchronous data query and retrieval;
Use JavaScript to tie everything together.
[Topic recommendation]:2020 ajax interview questions and answers (latest)
##2, Why use ajax:
2. What is the biggest feature of AJAX.
3. Please introduce the XMLhttprequest object.
4. What are the components of the AJAX technology system.
##HTML, css, dom, xml, xmlHttpRequest, javascript
In traditional Javascript programming, if you want to get information on the server-side database or file, or send client information to the server, you need to create an HTML form and then GET or POST data to the server. Users need to click the "Submit" button to send or receive data information, and then wait for the server to respond to the request and the page to reload.
Because the server returns a new page every time, traditional web applications may be slow and user-unfriendly.
Using AJAX technology, Javascript can interact directly with the server through the XMLHttpRequest object.
Through HTTP Request, a web page can send a request to the web server and accept the information returned by the web server (without reloading the page). The user is still shown the same page, and the user feels that the page is refreshed. , and you can't see the Javascript sending requests and receiving responses in the background.
There are a total of eight Callbacks for Ajax requests
onSuccess
onFailure
onLoading
onLoaded
onInteractive
onComplete
onException
Javascript is a scripting language that is executed on the browser side. Ajax is a development technology for creating interactive web applications. It uses a series of related technologies, including javascript.
Javascript is a scripting language developed by Netscape. It has nothing to do with Sun's Java language. Their similar names are just a marketing strategy.
In general web development, javascript is executed on the browser side. We can use javascript to control the behavior and content of the browser.
How information is passed between the browser and the server in an Ajax application
Through XML data or strings
The responseXMl attribute of the XMLHttpRequest object
Yes, it can be obtained through new ActiveXObject() in IE and through newXMLHttpRequest() in Firefox
10. Introduce the common methods and properties of the XMLHttpRequest object.
open("method","URL") establishes a call to the server. The first parameter is the HTTP request method, which can be GET, POST or anything supported by the server. The way you want to call it.
The second parameter is the URL of the requested page.
send() method, send a specific request
abort() method, stop the current request
readyState attribute request status is 5 Possible values 0=not initialized, 1=loading
2=to load, 3=interacting, 4=complete
responseText attribute The response of the server, represented as a string
reponseXML attribute server's response, expressed as XML
status HTTP status code of the server, 200 corresponds to ok and 400 corresponds to not found
12. What is XML
XML is an extended markup language that can describe data using a series of simple tags
##13. XML parsing methods
14. What framework (package) are you using?
This question is a must-ask, and is usually asked at the very beginning.15. If you are familiar with some kind of ajax framework , he may ask how to use this framework in the program
DWR framework introduction
16. Introduce what the $() function, $F() function, and $A() function of Prototype do.
$() method is A convenient shorthand for the all-too-frequently used document.getElementById() method in the DOM. Like this DOM method, this method returns the element with the id passed in as the parameter.17. Introduce the XMLHttpRequest object
Through the XMLHttpRequest object, Web developers can perform partial updates to the page after the page is loaded.18. What is the full name of AJAX? Introduce AJAX?
The full name of AJAX is Asynchronous JavaScript And XML.19. What technologies does Ajax mainly include?
Use JavaScript to bind everything together. In English, please see the original text by Jesse James Garrett, the proposer of Ajax, and the original title (Ajax: A New Approach to
AJAX applications use web browsers that support the above technologies as the running platform. These browsers currently include: Mozilla, Firefox, Internet Explorer, Opera, Konqueror and Safari. But Opera does not support XSL format objects, nor does it support XSLT.
20. What are the advantages and disadvantages of AJAX?
1. The biggest point is that the page does not refresh, and the user experience is very good.
2. Use asynchronous mode to communicate with the server, with faster response capability.
3. Some of the work previously burdened by the server can be transferred to the client, using the idle capacity of the client to process it, reducing the burden on the server and bandwidth, and saving space and broadband rental costs. And to reduce the burden on the server, the principle of ajax is to "fetch data on demand", which can minimize the burden on the server caused by redundant requests and responses.
4. Based on standardized and widely supported technology, there is no need to download plug-ins or small programs.
Disadvantages of ajax
1. Ajax does not support the browser back button.
2. Security issues AJAX exposes the details of interaction with the server.
3. The support for search engines is relatively weak.
4. Destroyed the exception mechanism of the program.
5. It is not easy to debug.
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