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<title>AJAX XMLHttpRequest Object</title>
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<p>From <b>http://www.w3schools.com</b> (Copyright Refsnes Data)</p>
<h1>AJAX - The XMLHttpRequest Object</h1>
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<h2>AJAX - More About the XMLHttpRequest Object</h2>
<p>Before sending data to the server, we have to explain three important
properties of the XMLHttpRequest object.</p>
<h3>The onreadystatechange Property</h3>
<p>After a request to the server, we need a function that can receive the data
that is returned by the server.</p>
<p>The onreadystatechange property stores the function that will process the
response from a server. The following code defines an empty function and sets
the onreadystatechange property at the same time:</p>
<table class="ex" width="100%" border="1" id="table6"><tr><td>
<pre>xmlHttp.onreadystatechange=function()
{
// We are going to write some code here
}</pre>
</td></tr></table>
<h3>The readyState Property</h3>
<p>The readyState property holds the status of the server's response. Each time the readyState changes,
the onreadystatechange function will be executed.</p>
<p>Here are the possible values for the readyState property:</p>
<table class="ex" border="1" width="100%" cellpadding="2" cellspacing="0" id="table7">
<tr><th align="left" width="10%">State</th><th align="left">Description</th></tr>
<tr><td>0</td><td>The request is not initialized</td></tr>
<tr><td>1</td><td>The request has been set up</td></tr>
<tr><td>2</td><td>The request has been sent</td></tr>
<tr><td>3</td><td>The request is in process</td></tr>
<tr><td>4</td><td>The request is complete</td></tr>
</table>
<p>We are going to add an If statement to the onreadystatechange function to test if
our response is complete (this means that we can get our data):</p>
<table class="ex" width="100%" border="1" id="table8"><tr><td>
<pre>xmlHttp.onreadystatechange=function()
{
if(xmlHttp.readyState==4)
{
// Get the data from the server's response
}
}</pre>
</td></tr></table>
<h3>The responseText Property</h3>
<p>The data sent back from the server can be retrieved with the responseText property.</p>
<p>In our code, we will set the value of our "time" input field
equal to responseText:</p>
<table class="ex" width="100%" border="1" id="table9"><tr><td>
<pre>xmlHttp.onreadystatechange=function()
{
if(xmlHttp.readyState==4)
{
document.myForm.time.value=xmlHttp.responseText;
}
}</pre>
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<p>The next chapter shows how to ask the server for some data!</p>
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<p>From <b>http://www.w3schools.com</b> (Copyright Refsnes Data)</p>
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