May 08, 2021 AJAX
Common AJAX interview questions and answers are listed below.
AJAX stands for Asynchronous JavaScript and XML. I t is a set of related techniques for displaying data asynchronously. In other words, it sends and retrieves data without reloading the page.
//创建 XMLHttpRequest 对象
var ajax = new XMLHttpRequest();
//规定请求的类型、URL 以及是否异步处理请求。
ajax.open('GET',url,true);
//发送信息至服务器时内容编码类型
ajax.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
//发送请求
ajax.send(null);
//接受服务器响应数据
ajax.onreadystatechange = function () {
if (obj.readyState == 4 && (obj.status == 200 || obj.status == 304)) {
}
};
5, ajax how to request? Their strengths and weaknesses?
Common post, get, delete. C opy, head, link, etc. are not commonly used.
Difference:
(1) Post is safer than get (because the post parameter is in the request body). get parameter above url)
(2) Get transmission speed is faster than post, according to the transfer. ( Post is received by requesting body ginseng, and in the background through the data stream.) I t's a little slower. And get is directly available via url ginseng)
(3) post transfer file big theory does not limit get transfer file small about 7-8k ie4k
(4) get to get data post upload data (upload more data and upload data are important data.) So both security and data magnitude post are the best options)
Synchronization requests block users until a response is retrieved, and asynchronous does not block users.
The important properties of the XMLHttpRequest object are given below.
onReadyStateChange
- Whenever the Readystate property changes, it is called.
readyState
the status of the request.
responseText
- It returns the response as text.
responseXML
- It returns a response in XML format.
status
- Returns the requested status number.
statusText
- Returns status details.
abort()
- used to cancel the current request.
getAllResponseHeaders()
Return title details.
getResponseHeader()
Return specific title details.
open()
- used to open the request.
send()
- used to send a request.
setRequestHeader()
- It adds a request header.
open(method,URL)
- It opens a request that specifies a get or post method and URL.
open(method,URL,async)
- it is the same as above but specifies asynchronous or not specified.
open(method,URL,async,userName,password)
- the same as above, but specifying a user name and password.
send()
- It sends a get request
send(string)
- Send a post request.
The callback function passes the function as an argument to another function. If we have to perform various AJAX tasks on the web site, then we can create a function for performing XMLHttpRequest and a callback function for each AJAX task.
JSON stands for JavaScript Object Notation. I n AJAX, it is used to exchange data between browsers and servers. I t's easy to understand that data is exchanged faster than XML. It supports arrays, objects, strings, numbers, and values.
request.onreadystatechange = function （）{
if（request.readyState == 4）
{
var jsonObj = JSON .parse（request.responseText）; // JSON.parse（）返回JSON对象
的document.getElementById（ “日期”）.innerHTML = jsonObj .date;
的document.getElementById（ “时间”）.innerHTML = jsonObj 。时间;
}
} There are several tools for debugging AJAX applications.
There are two types of postbacks in AJAX.
There are 5 requested readiness states in AJAX.
JUnit is the open source unit testing framework for client JavaScript. A test case needs to be created. A unit test case is a code that ensures that program logic works as expected.
| Javascript | Ajax |
|---|---|
| JavaScript is an object-based scripting language. | AJAX is a set of interrelated technologies such as JavaScript, XML, HTML, CSS, and so on |
| It requests the server and waits for a response. | It sends a request to the server without waiting for a response. |
| Reloading the page takes up more bandwidth. | It does not reload the page and therefore consumes less bandwidth. |