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Reading JSON files

From: JavaScript and AJAX

Video: Reading JSON files

Although AJAX was designed to work with files in the XML format, it will read the contents of any text file. So the data can really be in any format; the trick is to know how to parse or translate the data into objects that JavaScript can manipulate. An obvious choice is to use the file in the JSON format. JASON stands for JavaScript Object Notation, and is a way to structure data so that it can be easily converted to a JavaScript object. If you want to learn more about JSON, make sure you check out my course on Building Facebook Applications with HTML and JavaScript. There is a section called Adding JSON Data Feeds, and it has a good introduction to the JSON language.

Reading JSON files

Although AJAX was designed to work with files in the XML format, it will read the contents of any text file. So the data can really be in any format; the trick is to know how to parse or translate the data into objects that JavaScript can manipulate. An obvious choice is to use the file in the JSON format. JASON stands for JavaScript Object Notation, and is a way to structure data so that it can be easily converted to a JavaScript object. If you want to learn more about JSON, make sure you check out my course on Building Facebook Applications with HTML and JavaScript. There is a section called Adding JSON Data Feeds, and it has a good introduction to the JSON language.

So, let's go back and take a look at what a JSON document looks like. If you watch the movie on parsing XML using AJAX, this is the same data, but in a slightly different format. The good news is that parsing data is super simple--sort of; some browsers support a parse command, so let's go into the JavaScript file and replace the code for processing or XML file. So, I'm going to modify this open command to open the JSON document. Now I'm going to take out the rest of this code right here, and I'll create a variable called items and set it to the JSON object and use the parse command with the responseText of the request. Then I'll output this to the console so we can look at it.

So let me save this and I'll switch back to a browser, refresh our page, And if you have the console openm remember that you could just right-click on this page and select Inspect Element if you are using Google Chrome like me. And I can see the series of objects that this returns. If I open that up, I can see each individual object and inside each object, I can see different name and value pairs. So this is a little different from what we would see with XML. It's essentially an array of objects and each object has a label and the data from our file.

So here's the bad news: JSON parse is not available in some older browsers. So, if you go to this website, you could see that it's available in most modern browsers, but a lot of the older versions of IE do not support the parse command. So your options are to use EVAL--but that has some security issues--write your own parser, or use an existing library. jQuery for example, takes care of this very well. Let's go back to our code. So we'll modify our code so that it outputs a list of speakers. We'll start by creating the output variable, just like we did with XML, and then in here we'll loop through the valleys of the objects.

To do that I am going to use the for in statement. Finally, we'll target the update element with the results of our output variable. So let's save this and switch back to our browser, refresh the page, and you can see that the list appears. So working with JSON files is pretty easy with the parse command. However, it might not be available in all browser versions. So for ultimate compatibility, I recommend that you use a library like jQuery.

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JavaScript and AJAX

21 video lessons · 19511 viewers

Ray Villalobos
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