A data format widely used in Ajax is JSON -- this format is used to pass data from the web server to the browser, and it is in a format that is easily worked with in JavaScript.
We first need to take a look at the JSON format and how we can work with it, and then we'll see how this works together in Ajax.
The introduction to JSON from json.org is a great place to start:
JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate. It is based on a subset of the JavaScript Programming Language, Standard ECMA-262 3rd Edition - December 1999. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others. These properties make JSON an ideal data-interchange language.
JSON is built on two structures:
These are universal data structures. Virtually all modern programming languages support them in one form or another. It makes sense that a data format that is interchangeable with programming languages also be based on these structures.
FAQ
Let's take a look at the two data structures that JSON uses: objects and arrays.
In short, a JSON object is an unordered list of name/value pairs.
A JSON object example:
Note that the object (collection of name/value pairs) is enclosed in {curly braces}.
The name/value pair has a colon after the name (i.e. name: value), and the name/value pairs are separated by a comma.
So the object above represents the following:
| Name | Value |
|---|---|
| lastName | Faust |
| firstName | Drew |
| president@harvard.edu |
In short, a JSON array is an ordered sequence of values. Values are strings (in quotes), numbers, arrays, objects, or boolean (true/false) values.
A JSON array example
In the examples above, we've shown the values as strings (e.g. "Spring" or "Faust"). But values can also be arrays or objects. Below is a more complex JSON object that includes two name/value pairs whose values are an array of strings ("seasons") and the other an array of objects ("days"):
There are several online JSON viewers and validators you can use that are helpful for exploring, writing, or validating JSON structures:
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