Ajax basics and logon tutorials

Ajax basics and logon tutorials

Ajax is short for Asynchronous Javascript and XML.

Advantages of Ajax:

Advantage: reduces the burden on the server, obtains data on demand, and minimizes redundant requests.

Partial page refresh to reduce user psychology and actual waiting time, and bring a better user experience

Xml-based standardization, widely supported, and plug-ins not required

Further promote the separation of pages and Data

Ajax includes the following technologies:

Representation based on the web Standard (standards-based presentation) XHTML + CSS;

Use DOM (Document Object Model) 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 bind everything together.

That is to say, the biggest feature of Ajax is that it can achieve dynamic non-Refresh.

Use Ajax:

Example:

A table in the database:

Click to check whether the user name is available:

Homepage code:

<! DOCTYPE html> 
The processing page is as follows:

<? Php $ zhang = $ _ POST ["yhm"]; // value include ("db. class. php "); $ db = new db (); $ SQL =" select count (*) from mydb where zhang = '{$ zhang }'"; $ arr = $ db-> Query ($ SQL); echo $ arr [0] [0]; // The direct output is equivalent to the return result?>
Figure:
Enter an existing User Name:

Enter a user name that does not exist:

Then write a login:
Logon Page code:
<! DOCTYPE html> 
Next is the login processing page:
<? Phpinclude ("db. class. php "); $ db = new db (); $ zhang = $ _ POST [" zhang "]; $ mi = $ _ POST [" mi "]; // value: $ SQL = "select mi from mydb WHERE zhang = '{$ zhang}'"; $ arr = $ db-> Query ($ SQL ); if ($ arr [0] [0] ==$ mi &&! Empty ($ mi) {echo "OK" ;}else {echo "no" ;}?>
If the input is incorrect, the following message is displayed on this page:

Jump to the right of the input:

The advantage of using Ajax to write logs is that when an error is prompted, you do not need to jump to another page.
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