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Học php, mysql và javascript - p 41

Tham khảo tài liệu 'học php, mysql và javascript - p 41', công nghệ thông tin, đồ họa - thiết kế - flash phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Example 18-2. urlpost.html html head title Ajax Example title head body center h1 Loading a web page into a DIV h1 div id info This sentence will be replaced div script params url oreilly.com request new ajaxRequest request.open POST urlpost.php true request.setRequestHeader Content-type application x-www-form-urlencoded request.setRequestHeader Content-length params.length request.setRequestHeader Connection close request.onreadystatechange function if this.readyState 4 if this.status 200 if this.responseText null document.getElementById info .innerHTML this.responseText else alert Ajax error No data received else alert Ajax error this.statusText request.send params function ajaxRequest try var request new XMLHttpRequest catch e1 try request new ActiveXObject Msxml2.XMLHTTP catch e2 try request new ActiveXObject Microsoft.XMLHTTP catch e3 request false Using XMLHttpRequest 381 return request script body html Let s go through this document and look at what it does starting with the first three lines which simply set up an HTML document and display a heading. The next line creates an HTML DIV tag with the ID info containing the text This sentence will be replaced by default. Later on the text returned from the Ajax call will be inserted here. The next six lines are required for making an HTTP POST Ajax request. The first sets the variable params to a parameter value pair which is what we ll send to the server. Then the Ajax object request is created. After this the open method is called to set the object to make a POST request to geturl.php in asynchronous mode. The last three lines in this group set up headers that are required for the receiving server to know that a POST request is coming. The readyState property Now we get to the nitty-gritty of an Ajax call which all hangs on the readyState property. The asynchronous aspect of Ajax allows the browser to keep accepting user input and changing the screen while our program sets the onreadystatechange property to .