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In this example we're going to see how to use jQuery's AJAX features to deal with different kinds of data coming back from the server. Because data won't always be coming back in the form of HTML or text, sometimes it will be JSON, sometimes it will be XML, sometimes it will be binary format, jQuery's AJAX functions make dealing with different kinds of data pretty easy. Back here in the API documentation for jQuery, I am going to click on the Shorthand Methods again. Let's take a closer look at the jQuery.getJSON function.
getJSON is basically shorthand, which is equivalent to just calling the AJAX function that you can see here, with a dataType of json, a url, a data and a success function. And so here the arguments are, there is a url, and that's the url that you want to get the JSON data from. There is the data object, which is optional. It's the properties or data, or you can think of parameters that are sent to the server with the request, and then there is a success function, which is called when the function returns successfully.
Let's take a look at how we can use this in practice, so let's jump over to the code. Here in the code I have my DataTypes_start document open, and what we're going to do is first work with some JSON data. We're going to write a function called getJSON data when the document loads, and that's this function right here. Now, I have already put in a definition for the Flickr API. So, Flickr is an online photo service which provides a whole bunch of pictures, and it has a freely available JSON service where we can call the API provided by Flickr and get back photos that match a certain kind of tag.
Now, I am not going to go deep into how Flickr works. You can look it up on your own time. But we're going to use Flickr in this example because it has an option for providing JSON data. So what I am going to do is on the next line here, I am going to write $.getJSON, because we're going to get some JSON data. And the URL that we are going to use is this Flickr API URL right here. So I am going to pass that in as the first argument, so that's Flickr API, and then I need to provide some parameters to the Flickr API so it knows what photos I'm looking for.
I am going to pass in, first, I am going to ask for tags, which will be, let's see. Let's look for photos having to do with the space needle, and tag mode will be any. And again, these parameters are specific to Flickr. You can look up what these mean. And the format is going to be json, so we are telling Flickr that we want data back in JSON format. Let's assume that that works. What we are going to do then is call the successFn, and the successFn is down here.
When the successFn gets called, this result right here is not going to be a text string or HTML. It's going to be JSON, and it's going to be a JSON object. And so what I am going to do is use jQuery's each iterator to iterate over each one of the items that came back in the result set. Now again, this is going to be determined by what the structure of the JSON data that you get back is. Now, I happen to know that Flickr comes back with an items structure inside the result.
So for each thing in the result.items-- and I am going to declare a function that's going to handle each one of these and it's going to take an index and it's going to take the item itself. So for each one of these guys, what I am going to do is make a new image tag, and I am going to do that by using jQuery's HTML constructor to make a new image tag. And the image tag, I am going to give the attribute for the source. So I am going to set the source attribute for the image to item.media.m and again, this is specific to Flickr.
So, once I've set the attribute, I am going to take that image and I am going to append it to the content div. Once again just a review, make a new image, set the source attribute to the source inside the JSON structure for that particular item, and then append the whole thing to the content div, which is this guy right here, with the id of content. So, now I need to limit the number of photos I am getting back, because his is going to come back with a whole bunch of photos, and I don't want to do a whole bunch.
What I am going to do is say, if i == 4 then we're going to just return false, which tells this each iterator right here to stop running, and that should limit our results to just 4 photos. So, it looks like, if I've done this correctly, I am going to save this and now I am going to run it in the browser, okay. So let's go ahead and run this in my local server, and you can see that the API went out to Flickr and got a whole bunch of photos tagged with the space needle.
Now, these pictures are going to look different for you based upon when you run this example, so here you can see this is a pretty clear Space Needle photo. Here is one where it's way back in the background. The others are just Seattle. I am not sure why they came up, but they were tagged with Space Needle. So let's bring up the Developer Tools so that you can see what's happening. So here in the successFn, what I am going to do is put a breakpoint, and now I am going to refresh the page, and you can see there is the breakpoint being hit, all right, and here is the result.
Now you can see that the result is a JSON structure. This JSON structure is defined by Flickr. But you can see that there is an array of 20 things here in the items array, and each one of these is an object, right, and each object has a whole bunch of information about the picture and here is the media property, and there is the URL to the photo itself. So, what I am doing is I'm iterating over each one of these results.items set, and then for each item I'm building up the individual image.
So I'll take the breakpoint off and let it go, and we'll close the Developer Tools. Okay, so that's dealing with JSON data. Let's go back and take a look at how to deal with XML data, because XML data is another common piece of data that you work with on the Internet. So let's scroll back up. Then we'll comment out that function and call another one called getXMLData. And getXMLData is this function right here, so let's fill that one out. And for this example we're going to use our test XML data.XML file, and I just made this up. I threw some XML in here there is my name.
Here is the title, so this is what we're going to use. Back here on the code, let's write the code to get the XML data. In this case I am going to use $.get, and just get, I am not getting JSON here, so all I am going to do is ask for XML data, and I need to get the test xmldata.xml file. And this time I am going to write my own result function just right here inline. So I am going to write function result, and now we are going to flesh this out.
Now in this particular case when this function gets called, result is going to be an XML document. It's not going to be XML string data. It's not going to be text. It's going to be a parsed XML document, and that means I can use DOM XML functions on that result. For example, I can do things like var title = result. Because this is a document, I can say getElementsByTagName, and I will get to title first, and that comes back with an array, so we get the first one.
Okay, and then I'll do the same thing for var name =. And I'll just use this again, copy and paste, only this time I want the name. That gives me the tags for title and name, and now I am going to say var val = and I am going to say title.firstChild. nodValue. And again this is regular old XML, okay? In the title, the first child of this title tag is the text inside the tag.
That's just how the DOM works. So I am going to say + " by " + name.firstChild.nodeValue. So now I've got the title by name, and then all I need to do at that point is say $ and get a reference to my content div and say append that value.
Now, we're calling function when the document loads, so let's save this and watch what happens. So I am going to run this in my local server, and you can see it says jQuery Essential Training by Joe Marini, alright. Again, let's bring up Dev Tools so you can see what's happening. I am going to put a breakpoint right here inside the result function, and then I am going to refresh. And you can see that there is the breakpoint, okay. So, here is the result, right, and you can see that the result is a document. It's an XML document. So, jQuery correctly identified the incoming data as XML, parsed it into an XML document, which I can now use my XML DOM functions on.
So for example if I step over these functions, you'll see that title, right, is a node. That's a title tag, and name is a tag, right. Then when I step over this function, you can see that I now have a string that extracts the value of each one of the contents of those two tags, and then here is the content where I do the appending of the value into this div. So watch this area right here. So when I step, you can see that the string got put in there. In a nutshell, that's how you work with different kinds of data types using the jQuery AJAX functions.
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