Using XMLHttpRequest
Due to the differences between browser implementations of XMLHttpRequest
, itâs necessary to create a
special function in order to ensure that your code will work on all major
browsers.
To do this, you must understand the three ways of creating an
XMLHttpRequest
object:
IE 5:
request = new ActiveXObject("Microsoft.XMLHTTP")
IE 6+:
request = new ActiveXObject("Msxml2.XMLHTTP")
All others:
request = new XMLHttpRequest()
This is the case because Microsoft chose to implement a change with the release of Internet Explorer 6, while all other browsers use a slightly different method. Therefore, the code in Example 17-1 will work for all major browsers released over the last few years.
<script> function ajaxRequest() { try// Non-IE browser?
{ var request = new XMLHttpRequest() } catch(e1) { try// IE 6+?
{ request = new ActiveXObject("Msxml2.XMLHTTP") } catch(e2) { try// IE 5?
{ request = new ActiveXObject("Microsoft.XMLHTTP") } catch(e3)// There is no Ajax support
{ request = false } } } return request } </script>
You may remember the introduction to error handling in the previous
chapter, using the try...catch
construct. Example 17-1 is a perfect
illustration of its utility: it uses the try
keyword to execute the non-IE Ajax command
and, upon success, jumps on to the final return
statement, where the new object is
returned. If, however, the command fails, a catch
traps the error and the subsequent command is executed. Again, ...
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