hmc0316的部落格

這個常用到吔~~
by Justin Silverton

While working on an AJAX project over the weekend, I ran into the following issue: (through a GET request), every time I tried to call a certain function, It was returning the same data (which was supposed to be different each time)

I first tried the following (which should disable browser caching):

(in PHP)

header( “Expires: Mon, 26 Jul 1997 05:00:00 GMT” );
header( “Last-Modified: ” . gmdate( “D, d M Y H:i:s” ) . ” GMT” );
header( “Cache-Control: no-cache, must-revalidate” );
header( “Pragma: no-cache” );

The data still did not change.

I finally came to the following solutions:

1) use a POST request. When using with xmlhttprequest, it is slightly more complicated.

2) add a unique identifier to the end of my GET url.

I choose #2. A unique Identifier can be created using the current data+time. Here is a simple way to generate this (in Javascript):

var date = new Date();
var timestamp = date.getTime();

createXMLHttpRequest();
xmlHttp.onreadystatechange = handleMessages;
xmlHttp.open(”GET”,”script.php?time=”+timestamp,true);
xmlHttp.send(null);