JavaScript® 24-Hour Trainer

Chapter 33. Making Ajax Requests Using GET

Open a web browser and go to http://www.google.com. You've just sent a GET request to Google's webserver. Now point your browser to http://www.google.com/search?q=JavaScript. Once again you've sent a GET request to Google. Click any link in the search results. Yep, you just sent a GET request.

The HTTP protocol defines nine HTTP methods (also known as verbs) that determine what type of action is taken on the requested resource. The GET verb indicates that the client requesting a resource simply wants to get the data that the resource contains. GET requests are typically thought of as safe requests because they're not meant to cause any change on the server; they are simply used to request a resource's data.

As mentioned in Lesson 32, there are two types of requests you can make with XMLHttpRequest (XHR) objects: GET and POST. The majority of requests users make on the Internet are GET requests. Similarly, the majority of requests you'll make with XHR will be GET requests.

MAKING GET REQUESTS

Code samples in Lesson 32 illustrated how you make GET requests, but let's go over everything you need to make these types of requests. First, you create the XHR object and initialize it with the open() method, like this:

var xhr = createXHR();

xhr.open("GET", "info.txt");

The first argument passed to open() tells the XHR object to make a GET request to the URL specified as the second argument, and since the third argument is omitted, the request is sent ...