Detailed explanation of JavaScript object serialization_javascript skills

1. What is object serialization?

Object serialization refers to converting the state of an object into a string (from my rookie understanding, it seems that some books also say this, it is easy to understand!);

Serialization is the process of converting the state information of an object into a form that can be stored or transmitted (from "Baidu Encyclopedia - Serialization", highly academic and slightly high-end);

2. Why is there object serialization?

Everything in the world has a reason for its existence. Why is there object serialization? Because programmers need it. Since it is object serialization, let’s start with an object:

var obj = {x:1, y:2};

When this code is run, the contents of the object obj will be stored in a piece of memory, and obj itself only stores the mapping of the address of this memory. Simply put, object obj is something that our program maintains in memory when the computer is powered on. If our program stops or the computer is powered off, object obj will no longer exist. So how to save the contents of object obj on the disk (that is, keep it when the power is out)? At this time, you need to serialize the object obj, that is, convert the content of obj into a string form, and then save it on the disk. In addition, how do we send the content of object obj to the client through HTTP protocol? Yes, you still need to serialize the object obj first, and then the client deserializes the received string (that is, restores the string to an object) to parse out the corresponding object. These are exactly the two functions described in "Baidu Encyclopedia - Serialization" - storage and transmission.

3. Object serialization in JavaScript

The full name of JSON is "JavaScript Object Notation" - JavaScript object notation. ECMAScript 5 provides built-in functions JSON.stringify() and JSON.parse() to serialize and restore JavaScript objects. They're also easy to use:

As you can see, there is no y:undefined content in exampleStr and exampleObj2. This shows that: JSON syntax is a subset of JavaScript syntax. It cannot represent all values ​​in JavaScript. For attributes that are not supported by JSON syntax, they will be omitted after serialization. The detailed rules are as follows:

• ① For the five primitive types in JavaScript, JSON syntax supports four types: numbers, strings, Boolean values, and null. Undefined is not supported;
• ②The result of NaN, Infinity and -Infinity serialization is null;
• ③JSON syntax does not support functions;
• ④In addition to RegExp and Error objects, JSON syntax supports all other objects;
• ⑤The result of serialization of date objects is strings in ISO format, but JSON.parse() still retains their string form and will not restore them to date objects;
• ⑥JSON.stringify() can only serialize the enumerable own properties of the object;

As can be seen from the above example, if the above rules are met, deep copying of objects can also be completed through object serialization and deserialization.

The above are the common uses of JSON.stringify() and JSON.parse(), but these two methods are not just that simple:

4. Full version JSON.stringify()

1. Introduction

Serialize primitive value, object or array

2. Summary

JSON.stringify(o[, filter][, indent])

3. Parameters

o, the original value, object or array to be converted into a JSON string

Filter, optional parameter, an array or function

indent, optional parameter, a value or a string

4. Return

A string in JSON format, representing the value of o, which has passed the filter and is formatted according to indent

5. Description

　①When object o itself has a toJSON() method, JSON.stringify() will call o's toJSON() method and use the return value of the method instead of the object itself for stringification;

　②If filter exists and is a function, the return value of the function will be used as the return value of the JSON.stringify() method. And this function receives two parameters, the first parameter is an empty string, and the second parameter is the object o.

　③If filter exists and is a string array (if the array contains numbers, the numbers will be automatically converted to strings), then if some attribute names of object o are not in this array, these will be serialized during serialization. The attributes are omitted, and the order of the attributes in the returned string will be consistent with the order of the attributes in the array;

　④JSON.stringify() usually returns a string without any spaces or newlines. If you want to output a more readable string, you need to specify the third parameter. If the specified third parameter is a value between 1 and 10, JSON.stringify() will insert newlines and the specified number of spaces in the output of each "level". If the specified third parameter is a non-empty string, JSON.stringify() will insert a newline character and the string (only the first ten characters are taken) to indent the level;

5. Full version JSON.parse()

1. Introduction

Parse strings in JSON format

2. Summary

JSON.parse(s[, reviver])

3. Parameters

s, the string to be parsed

Reviver, optional parameter, optional function used to convert parsed values ​​

4. Return

An object, array or primitive value. The return value is parsed from s (and may be modified by reviver);

5. Description

　①If the reviver function is specified, this function will be called once for each original value parsed from s (not the object or array containing these original values). There are two parameters when calling reviver. The first parameter is the attribute name - the attribute name of the object or the array number converted into a string. The second parameter is the original value of the object attribute or array element. Moreover, the return value of the reviver function will be used as the return value of JSON.parse();

The above is the relevant content about JavaScript object serialization. I hope it will be helpful to everyone's learning.