Why ajax

Note: If you do not set header Cache-Control: no-cache the browser will cache the response and never re-submit the request, making debugging challenging. You can also add an always-different GET parameter, like a timestamp or random number see bypassing the cache. Note: If the httpRequest variable is used globally, competing functions calling makeRequest can overwrite each other, causing a race condition. In the event of a communication error such as the server going down , an exception will be thrown in the onreadystatechange method when accessing the response status.

To mitigate this problem, you could wrap your if In the previous example, after receiving the response to the HTTP request we used the request object's responseText property , which contained the contents of the test.

Now let's try the responseXML property. First off, let's create a valid XML document that we'll request later on. The document test. Then in alertContents , we need to replace the line alert httpRequest.

Finally, let's send some data to the server and receive a response. Our JavaScript will request a dynamic page this time, test. We'll also add a line to our event handler to get the user's data from the text box and send it to the makeRequest function along with the URL of our server-side script:.

We need to modify makeRequest to accept the user data and pass it along to the server. The function alertContents can be written the same way it was in Step 3 to alert our computed string, if that's all the server returns. However, let's say the server is going to return both the computed string and the original user data. Your message has been sent to W3Schools. W3Schools is optimized for learning and training. Examples might be simplified to improve reading and learning.

Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. While using W3Schools, you agree to have read and accepted our terms of use , cookie and privacy policy. Adjusting the width could make a callback to the server to set the session variable for the new width. Otherwise, the object would go back to its initial default width. Other features include text hints and autocomplete text boxes.

The client types in a couple of letters and a list of all values that start with those letters appear below. A callback is made to a web service that will retrieve all values that begin with these characters.

This is a fantastic feature that would be impossible without Ajax and is also part of the Ajax Control Toolkit. Segue recently used Ajax to support a client application that had problems due to limited bandwidth and page size. The combination caused the application to take too long to retrieve data and display it on the page.

Sometimes, the web server would simply not have the resources to handle the request and timeout. The best solution for this issue was Ajax. To solve this problem, we created JSON Web Services on the web server in order to retrieve the details about the selected item.

Instead of posting back to the server, the client would call the web service when an item was selected from the list box.