Basic operations examples of JSON objects in JavaScript _ basics

JSON object

1, the properties of the object:
the properties of an object are composed of key-value pairs, where key is a string and value can be any JavaScript object.

Use [] to set and get properties of an object
var obj = new Object ();
obj["www.jb51.net"] = "http://www.jb51.net";
Alert (obj["www.jb51.net"]);

2. Variables are both attributes:
the JavaScript engine constructs a global object when initialized, and all variables are properties of this global object. To refer to this global object, you can then get this in the top-level scope:

var global = this;

In JavaScript, any independent function or variable belongs to the object's properties, namely:

function Test () {}

Equivalent:

Window.test = function () {}

3, the use of the object:
three ways to declare an object:

① creates an object object by using the new operator, and then dynamically adds the property, creating a target from scratch
② defines the class circle of the object, and then uses the new operator to bulk construct the object

Create an object
function User (username, password) {
  this.username = Username;
  This.password = password;
  This.getusername = function () {return
    this.username;
  }
  This.getpassword = function () {return
    this.password;
  }
}
var arthinking = new User ("Jason", "123");
Alert (Arthinking.getusername ());
Alert (Arthinking.getpassword ());

③ using JSON to construct objects
JSON is the JavaScript object representation method (JavaScript Object notation), which means that an object is represented by a literal amount:

JSON form to create an object
var arthinking = {
  username: "Jason",
  Password: "123",
  favorite: {
    sports: "F Ootball ",
    Music:" Guitar "
  }
alert (arthinking.username);
alert (arthinking.favorite.sports);

Resolves JSON-formatted data returned by the server
a single JSON object:

[{A: ' 1 ', B ' 2 '},{a: ' 3 ', B ' 4 '}]

Multiple JSON objects:

{
"usergroups": [{a: ' 001 ', B: ' arthinking '},a: ' 002 ', B: ' Jason '}],
"groups": [{c: ' 001 ', D: ' It Curtilage '}]
}

Can be based on this format from the background to encapsulate the need to pass the data, the foreground can be obtained after the resolution to obtain data:

Suppose Response.responsetext
converts a JSON string to a JavaScript statement//by using the Eval () function for the returned JSON string//
and then through "." Navigate to get the specific properties, the length property is the lengths of the object
var obj = eval ("+ Response.responsetext +"));
for (var i = 0; i<obj.usergroups.length; i++) {
  var groupid = obj.usergroups[i].a;
  var usergroup=obj.groups;
  for (var j=0; j<usergroup.length; J + +) {
    if (usergroup[j].c = = GroupID) {
      alert (groupid);}
  }}