What is JSON and why would I use it? Json vs XML

d

JSON (JavaScript Object Notation) is a lightweight format that is used for data interchanging. It is also a subset of JavaScript's Object Notation (the way objects are built in JavaScript) An example of where this is used is web services responses. In the 'old' days, web services used XML as their primary data format for transmitting back data, but since JSON appeared (The JSON format is specified in RFC 4627 by Douglas Crockford), it has been the preferred format because it is much more lightweight You can find a lot more info on one of Crockford's sites here JSON is built on two structures: A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array. An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence. JSON Structure Here is an example of JSON data: { "firstName": "John", "lastName": "Smith", "address": { "streetAddress": "21 2nd Street", "city": "New York", "state": "NY", "postalCode": 10021 }, "phoneNumbers": [ "212 555-1234", "646 555-4567" ] } JSON in JavaScript When working with JSON and JavaScript, you may be tempted to use the eval function to evaluate the result returned in the callback, but this is not suggested due to security reasons (malicious data can be sent from the server to the client and then evaled in the client script with harmful effects). Therefore, one must always try to use Crockford's script that checks for a valid JSON before evaluating it. Link to the script explanation is found here and here is a direct link to the js file. Example on how to use the JSON Parser (with the json from the above code snippet): //The callback function that will be executed once data is received from the server var callback = function (result) { var johnny = JSON.parse(result); //Now, the variable 'johnny' is an object that contains all of the properties //from the above code snippet (the json example) alert(johnny.firstName + ' ' + johnny.lastName); //Will alert 'John Smith' }; The JSON Parser also offers another very useful method, stringify. This method accepts a JavaScript object as a parameter, and outputs back a string with JSON format. This is useful for when you want to send data back to the server: var anObject = {name: "Andreas", surname : "Grech", age : 20}; var jsonFormat = JSON.stringify(anObject); //The above method will output this: {"name":"Andreas","surname":"Grech","age":20} The above two methods (parse and stringify) also take a second parameter, which is a function that will be called for every key and value at every level of the final result, and each value will be replaced by result of your inputted function. (More on this here) Btw, for all of you out there who think JSON is just for JavaScript, check out this post that explains and confirms otherwise. JSON Tutorial available http://www.w3schools.com/json/ References JSON.org Wikipedia Json in 3 minutes (Thanks mson) Using JSON with Yahoo! Web Services (Thanks gljivar)