Detailed explanation of JavaScript basics

This article mainly introduces relevant information about the basic knowledge of JavaScript (JSON, Function objects, prototypes, reference types). It is very good and has reference value. Friends who need it can refer to it. I hope it can help everyone.

1. JSON

# Concept: JavaScript Object Notation (JavaScript Object Notation) is a lightweight data exchange format

Features: easy for programmers to write and view; easy for computers to parse and generate

Data structure: Object object format { key: value, key: value}

Array array format [ value , value ]

Eg: var json = ' { " " : '' '' } ' (inner double quotes, outer single quotes)

* JSON - supports independent ".json "File; allows nesting

JSON format is supported by almost all mainstream development languages---the consensus of each grammar language is that strings

Strings in JSON can only use double quotes

* Supported data types: string; number; boolean; null; object; array

Convert JSON objects and strings

Convert to JSON objects: JSON.parse(object ) ---(Server=>Client), parse JSON string,

convert to JSON string: JSON.stringify(string) ---- (Client=>Server),

2. Function object

Function and Function object:

The Function type is one of the reference types provided by JavaScript; an object of Function type is created through the Function type. The object is actually a [function].

var object name = new Object( ); ---Create object

var function name = new Function( ); // function anonymous( ){}

【 In JavaScript, all functions are objects of Function】

var function name = new Function (parameter, function body);

The last parameter in the brackets ( ) is recognized as the function body, except These are all formal parameters. ---Not recommended

Constructor:

Function: To create objects (factory method)

Syntax structure:

function 构造函数名称（形参）{
 this.属性名 = 属性值;    ---- this的含义 -> 指的是创建的对象
 this.方法名 = function( ){ }   
}
var 对象名 = new 构造函数名称( );

3, prototype

In JavaScript, a function is an object of type Function that contains properties and methods.

Attribute (Prototype) already exists when the function is defined. It is a predefined attribute of the Function object (i.e. function); its initial value is an empty object. There is no prototype type defined for a function in JavaScript, so the prototype can be of any type.

The prototype is used to save the shared properties and methods of the object. The properties and methods of the prototype do not affect the properties and methods of the function itself.

² Explicit prototype - Function's prototype

is used in a real development environment

² Implicit prototype - Function's __proto__

is used Tests during the development process cannot be used in the real development environment

4. Reference type

Data type:

Number-define numbers by creating objects; String -Define numbers by creating objects;

Boolean-Define numbers by creating objects;

Date type

Function: Get regular date + time

getFullYear(): Get the year; getMonth(): Get the month; getDate(): Get the date

getTime (): The time and date from January 1, 1970 to the present [Use millisecond values ​​to calculate time Calculation; implement timestamp (identification)]

eg: The date format is the current time on YYYY year MM month DD day

var date = new Date( );
console.log(date.getFullYear( ) + '年' + date.getMonth( ) + '月' + date.getDay( ) + '日');

Math type

Attribute: PI - Pi Note: No need to create an object

Method: Processing of numbers

ceil(x): round up to integer; floor(x): round down to integer or round; round(x) ): Rounding

pow(x1, x2): n1 to the n2 power random(): Generate a random number between 0-1

eg: 0-100 random number console.log (Math.random( )*100);

1-100 random integer console.log(Math.random( )*99+1);

20% probability of executing one, 50% Probability execution 2 if( num ##                                                                                                      ##Global object: global properties (Infinity, NaN, undefined), global methods, which can be called anywhere in JavaScript.

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