javascript

Chapter 17: Ajax and JSON
This syntax represents a data object with four properties. Each property name must be enclosed in
double quotes, and each value may be a string, a number, a Boolean, null , an object, or an array. The
data - object format is also a valid object literal in JavaScript and can be assigned directly to a variable, as
in this example:
var person = {
“name”: “Nicholas C. Zakas”,
“title”: “Software Engineer”,
“author”: true,
“age”: 29
};
Note that although JavaScript doesn ’ t require object properties to be quoted, unquoted property names
are considered a syntax error in JSON.
Arrays are represented in JSON using the array - literal syntax from JavaScript. Here’s an example:
[ 1, 2, “color”, true, null]
Each value in an array may be a string, a number, a Boolean, null , an object, or an array. You can, for
instance, create an array of objects describing people, as follows:
[
]
{
},
{
}
“name”: “Nicholas C. Zakas”,
“title”: “Software Engineer”,
“author”: true,
“age”: 29
“name”: “Jim Smith”,
“title”: “Salesperson”,
“author”: false,
“age”: 35
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Keep in mind that this is plain text, not JavaScript code. The idea is to format data into a JSON structure
on the server and pass it to the browser. Since JSON is a valid JavaScript representation for objects and
arrays, a string of JSON data can be passed into the eval() function to return an object or array instance.
For example, if the previous code were contained in a variable named jsonText , the following code
would provide access to that data:
//evaluate into an array
var people = eval(jsonText);
//access data
alert(people[0].name);
people[1].age = 36;
if (people[0].author){
alert(people[0].name + “ is an author”);
}