Updating web pages with ajax

Of course your own pages may execute functions on user interaction, but for the purposes of this demonstration add the following script at the end of your page, before the closing body tag: The script first checks that the browser supports the Event Source model.If it doesn’t, an error message is written to the server data page element instead.Then the script sets up an event listener function to execute when the Event Source object receives an update from the server.When this happens, the script simply gets a reference to the update page element and writes the new data to it.

In this tutorial we have carried out the basics of using Server-Sent events with HTML5, Java Script and PHP.With Server-Sent requests, you can stream data from your server, with updates pushed from there without the code at client side having to keep requesting it.Once your page initiates the Server-Sent event, the server script can continue sending updates.Image updating is useful if you have dynamic graphs or perhaps a webcam. The main trick is appending a date string after the image file name to make sure the browser does not use a cached version of the image.A simple bit of javascript can be used to request the browser to reload a new image at regular intervals. As the date string is appended as a The following files provide a simple demonstration of AJAX.We now need to create the server side PHP script to send updates to the page.Create a new file and save it “send_sse.php” or another name of your choice, as long as you amend the Java Script Event Source code above to reflect the correct name and location.If the browser does support the function, the Server-Sent process begins.First, the script creates an object of the Event Source class, passing it the URL of the server side script that will be providing the streamed data updates.For example, if you are regularly dynamically creating a new graph image, you need to make sure a half saved version of the image file is not served to a browser.If this happens, the browser will display a corrupt image, or nothing at all.

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