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JavaScript: Tutorial - A Guide to JavaScript - Page 21

JSON

JSON, JavaScript Object Notation, is a data format and not a programming language.

Syntax

• Simple Values: Strings, numbers, Booleans, and null can all be represented in JSON using the same syntax as JavaScript. The special value undefined is not supported.
• Objects: The first complex data type, objects represent ordered key-value pairs. Each value may be a primitive type or a complex type.
• Arrays: The second complex data type, arrays represent an ordered list of values that are accessible via a numeric index. The values may be of any type, including simple values, objects, and even other arrays.

Objects

The difference between JavaScript strings and JSON strings is that JSON must use double quotes to be valid.

A JavaScript object literal looks like this:

var object = {
	name: "Dave",
	age: 39
};

This is the same as the previous example.

var object = {
	"name": "Dave",
	"age": 39
};

Now in JSON.

{
	"name": "Dave",
	"age": 39
}

You can embed objects within objects.

{
	"name": "Dave",
	"age": 39,
	"address": {
		"street": "123 Abc Ln.",
		"city": "Austin",
		"state": "Texas",
		"country": "United States"
	}
}

Arrays

This is an array in JSON.

[42,"hello",false]

This is an array in JavaScript (very similar).

var arrayObj = [42,"hello",false]; 

Arrays and object can be used together.

[
	{
		"title": "Professional ASP.NET MVC 1.0",
		"authors": [
			"Rob Conery",
			"Scott Hanselman",
			"Phil Haack",
			"Scott Guthrie"
		],
		"edition": 1,
		"year": 2011
	},
	{
		"title": "Professional ASP.NET MVC 2.0",
		"authors": [
			"Jon Galloway",
			"Rob Conery",
			"Scott Hanselman",
			"Phil Haack",
			"Scott Guthrie"
		],
		"edition": 1,
		"year": 2012
	},
	{
		"title": "Professional ASP.NET MVC 3.0",
		"authors": [
			"John Galloway",
			"Brad Wilson",
			"Phil Haack",
			"K. Scott Allen"
		],
		"edition": 1,
		"year": 2013
	},
	{
		"title": "Professional ASP.NET MVC 4.0",
		"authors": [
			"John Galloway",
			"Brad Wilson",
			"Phil Haack",
			"K. Scott Allen"
		],
		"edition": 1,
		"year": 2014
	}
]

JSON Object

The JSON object has two methods, stringify() and parse().

var person = {
	lastname: "Hughes",
	firstname: "John",
	relatives: [
		"JoAnn Hughes"
		"Jim Hughes"
		"Simon Hughes"
	],
	street: "123 Abc Ln.",
	city: "Austin",
	state: "Texas",
	zip: "78705"
};
var JsonString = JSON.stringify(person); // strip all the white space out

This example serializes a JavaScript object into a JSON string.

A JSON string can be passed directly into JSON.parse() and it creates a JavaScript value. To create an object similar to the person object:

var personObj = JSON.parse(JsonString);

Filtering Results

If the second argument to JSON.stringify() is an array, then it will include only object properties that are listed in the array.

var person = {
	lastname: "Hughes",
	firstname: "John",
	relatives: [
		"JoAnn Hughes"
		"Jim Hughes"
		"Simon Hughes"
	],
	street: "123 Abc Ln.",
	city: "Austin",
	state: "Texas",
	zip: "78705"
};
var JsonString = JSON.stringify(person, ["street", "city", "state", "zip"]); // create a JSON string with just the address

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