Objects and JSON in JavaScript_Basics

Introduction

JSON is JavaScript Object Natation. It is a lightweight data exchange format that is very suitable for the interaction between the server and JavaScript.
JSON is a data exchange format, like XML and YAML, a way to transfer structured information between various languages. On the other hand, JavaScript objects are a data type in the JavaScript language, just like arrays in PHP, classes and structures in C.

Define JSON and javascript objects

When defining an object in a JavaScript program, the attribute name of the object can be enclosed in double quotes or not. If the attribute name contains special characters (such as!, if, etc.), double quotes must be added.
When defining JSON, the attribute name must be enclosed in double quotes.

Code example:

1. Define javascript object

Copy code The code is as follows:

var obj={name:"tudouya","sex":"man"}; #Two attributes can be added with double quotes or without
var obj={"!":"hello world"}; #Double quotes must be added when the attribute name contains special characters

2. Define JSON string

Copy code The code is as follows:

var jsonString={"name":"tudouya"}; #Double quotes must be added when defining JSON

javascript object converted to JSON

1. Convert javascript object to JSON

We can use javascript’s built-in function to convert javascript objects to JSON. This function is JSON.stringify().
Code example:

Copy code The code is as follows:

var obj={name:"tudouya",sex:"man"};
var jsonObj=JSON.stringify(obj);
console.log(jsonObj);
##The output result is: {"name":"tudouya","sex":"man"}

When converting JavaScript objects to JSON, there is one thing we need to pay attention to:
If the object contains attributes whose values ​​are functions and dates, JSON ignores the attributes whose values ​​are functions and converts the attributes whose values ​​are dates into strings.
Code example:

Copy code The code is as follows:

var obj={
name:"tudouya",
birthday:new Date(),
action:function (){
document.write("walk");
}
};
var jsonObj=JSON.stringify(obj);
console.log(jsonObj);
##The output result is: {"name":"tudouya","birthday":"2014-08-12T10:05:00.497Z"}

Parsing JSON in javascript

In older versions of JS, everyone usually uses the eval() function to parse JSON, but ECMAScript5 provides us with a new function JSON.parse() for parsing JSON.

The use of this function is relatively simple, you can try it yourself. When this function is applied to a JSON string, the JSON is converted into a JavaScript object. That is to say, when the typeof operator is used to view the type of the function, the returned value is Object.
Another thing to note is that this function is only supported after ECMAScript 5. If it is an older version of the browser, it may not support this function. The solution is to load a js file that implements this function, namely json2.js. If you are using the JQuery framework, jQuery.parseJSON(), this function calls the JSON.parse() method.
Regarding using the eval() method to parse JSON, this will be recorded after in-depth study.

A very important concept

As a front-end rookie, I often hear people say "JSON object", but in fact there is no concept of "JSON object". The real form of JSON is a string.