How do I make a JSON object with multiple arrays?

Question

I've never used JSON before so I'm not familiar with its syntax.

At the moment I have multiple arrays containing different pieces of data.

I would like to create one JSON object, that contains the multiple arrays each with several pieces of data.

E.g.

An object called cars, containing multiple arrays each for a different make of car. In each array would be the model of car along with some other types of data e.g. number of doors (doesn't really matter its just a fictional example.)

It would be greatly appreciated if someone explained the syntax with an example.

Answer 1

On the outermost level, a JSON object starts with a { and end with a }.

Sample data:

{     "cars": {         "Nissan": [             {"model":"Sentra", "doors":4},             {"model":"Maxima", "doors":4},             {"model":"Skyline", "doors":2}         ],         "Ford": [             {"model":"Taurus", "doors":4},             {"model":"Escort", "doors":4}         ]     } } 

If the JSON is assigned to a variable called data, then accessing it would be like the following:

data.cars['Nissan'][0].model   // Sentra data.cars['Nissan'][1].model   // Maxima data.cars['Nissan'][2].doors   // 2  for (var make in data.cars) {     for (var i = 0; i < data.cars[make].length; i++) {         var model = data.cars[make][i].model;         var doors = data.cars[make][i].doors;         alert(make + ', ' + model + ', ' + doors);     } } 

Another approach (using an associative array for car models rather than an indexed array):

{     "cars": {         "Nissan": {             "Sentra": {"doors":4, "transmission":"automatic"},             "Maxima": {"doors":4, "transmission":"automatic"}         },         "Ford": {             "Taurus": {"doors":4, "transmission":"automatic"},             "Escort": {"doors":4, "transmission":"automatic"}         }     } }  data.cars['Nissan']['Sentra'].doors   // 4 data.cars['Nissan']['Maxima'].doors   // 4 data.cars['Nissan']['Maxima'].transmission   // automatic  for (var make in data.cars) {     for (var model in data.cars[make]) {         var doors = data.cars[make][model].doors;         alert(make + ', ' + model + ', ' + doors);     } } 

Edit:

Correction: A JSON object starts with { and ends with }, but it's also valid to have a JSON array (on the outermost level), that starts with [ and ends with ].

Also, significant syntax errors in the original JSON data have been corrected: All key names in a JSON object must be in double quotes, and all string values in a JSON object or a JSON array must be in double quotes as well.

See:

• JSON specification
• JSONLint - The JSON validator

Answer 2

A good book I'm reading: Professional JavaScript for Web Developers by Nicholas C. Zakas 3rd Edition has the following information regarding JSON Syntax:

"JSON Syntax allows the representation of three types of values".

Regarding the one you're interested in, Arrays it says:

"Arrays are represented in JSON using array literal notation from JavaScript. For example, this is an array in JavaScript:

var values = [25, "hi", true]; 

You can represent this same array in JSON using a similar syntax:

[25, "hi", true] 

Note the absence of a variable or a semicolon. Arrays and objects can be used together to represent more complex collections of data, such as:

{     "books":               [                 {                     "title": "Professional JavaScript",                     "authors": [                         "Nicholas C. Zakas"                     ],                     "edition": 3,                     "year": 2011                 },                 {                     "title": "Professional JavaScript",                     "authors": [                         "Nicholas C.Zakas"                     ],                     "edition": 2,                     "year": 2009                 },                 {                     "title": "Professional Ajax",                     "authors": [                         "Nicholas C. Zakas",                         "Jeremy McPeak",                         "Joe Fawcett"                     ],                     "edition": 2,                     "year": 2008                 }               ] } 

This Array contains a number of objects representing books, Each object has several keys, one of which is "authors", which is another array. Objects and arrays are typically top-level parts of a JSON data structure (even though this is not required) and can be used to create a large number of data structures."

To serialize (convert) a JavaScript object into a JSON string you can use the JSON object stringify() method. For the example from Mark Linus answer:

var cars = [{     color: 'gray',     model: '1',     nOfDoors: 4     },     {     color: 'yellow',     model: '2',     nOfDoors: 4 }]; 

cars is now a JavaScript object. To convert it into a JSON object you could do:

var jsonCars = JSON.stringify(cars); 

Which yields:

"[{"color":"gray","model":"1","nOfDoors":4},{"color":"yellow","model":"2","nOfDoors":4}]" 

To do the opposite, convert a JSON object into a JavaScript object (this is called parsing), you would use the parse() method. Search for those terms if you need more information... or get the book, it has many examples.