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First knowledge of Web Design

2022-07-27 02:15:00 【Although there are delicacies】

In Web Design , Web pages are usually divided into three levels ： The structure layer (HTML), The presentation layer (CSS), Behavior layer (Javascript).
One 、HTML、CSS、JavaScript brief introduction

1、 What is? HTML

HTML（ Hypertext markup language  Hyper Text Markup Language） It's a language used to describe Web pages . It includes a series of labels ． With these tags, you can put Unified document format , To disperse Internet The resource is connected as a Logical whole .HTML Text is created by HTML Descriptive text composed of commands ,HTML Command descriptive text , graphics 、 Animation 、 voice 、 form 、 Links, etc. .


2、 What is? CSS

CSS( Cascading style sheets  Cascading Style Sheets) It's a form of expression HTML（ An application of Standard General Markup Language ） or XML（ A subset of Standard General Markup Language ） Such as file style Computer language .CSS Not only can Statically decorate Webpage , It can also cooperate with various scripting languages to dynamically analyze the elements of web pages format .     

Style definition display HTML The syntax of the element is ：selector {property：value} ( Selector { attribute ： value })


3、 What is? JavaScript

JavaScript It's a kind of Scripting language , Its source code does not need to be compiled before it is sent to the client to run , Instead, send the character code in text format to browser The browser explains that running it can realize complex functions on Web pages , Web pages no longer show you simple static information , But real-time content updates , Interactive maps ,2D/3D Animation , Scrolling videos and so on .

From a macro point of view ,HTML Define the structure of the web page ,CSS Describe the appearance of web pages ,JavaScript Set the behavior of the web page . for instance , If a web page is compared to a person ,HTML Is a person's body , and CSS It's people's clothes , These constitute a vegetable , add javascript Vegetative people can respond to external stimuli , Produce behavior , Become a real person .

Through the body of the web HTML These three can be linked ,HTML It's a description language , Through the browser to achieve , The details are as follows ：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title> Webpage title </title>
<link rel="stylesheet" type="text/css" href="mycss.css" />
<script type="text/javascript" src="myjs.js"></script>
</head>
<body>
<p> My first web page </p>
</body>
</html>

This is the simplest Single HTML file , The document says , browser , I follow W3C standard XHTML1.0 Transitional version specification （ Document type declaration ）, The code used is utf-8, My title is “ Webpage title ”, The stylesheet describing my appearance is my same catalog mycss.css file , It's about me javascript The code is at my level myks.js In file , My content has a paragraph , The content of the paragraph is “ My first web page ”. 


Two 、HTML、CSS、JavaScript Development
1、HTML Version of

Now it's commonly used HTML 4.01 and HTML5.2000 International World Wide Web Consortium （W3C） Published XHTML 1.0 edition .XHTML 1.0 It's a kind of HTML 4.0 Based on the optimization and improvement of the new language , The purpose is based on XML application . and XHTML And HTML 4.01 It's almost the same ,HTML From the beginning to XHTML Become more rigorous in the process , More flexible , And CSS The combination is better . In principle, most of the web pages you can see now use HTML4 perhaps HTML5 These two versions of .
 

HTML5 It's right HTML Major changes , although HTML5 The standard is still being worked out , But it cannot hinder its unstoppable pace .HTML5 See 《HTML5 Introduction and in-depth understanding 》

2、CSS Version of （Level）


CSS2.1 yes W3C Now we are recommending ;
CSS3 It is still under development .
if HTML The development of is a process of constant revision , that CSS The development of is a process of continuous supplement , So it's using CSS When , No need to be like HTML That line states the standard used , High version browsers recognize high version CSS Definition , The lower version of the browser skipped the unknown CSS Definition . No matter what version ,CSS The grammar of is very simple , Selectors ：{ attribute ： Property value }, So hot CSS3 Nothing more than extending selectors and properties .
CSS3 See 《CSS3 New selectors and properties 》

3、JavaScript The past and this life

JavaScript A literal script language , Its interpreter is called JavaScript engine , It's part of the browser , namely ：JavaScript It is interpreted and executed by the browser of the client , So I'm talking about JavaScript Before we talk about the history of browser . One of the earliest web The browser was created in 1991 Year of WorldWideWeb, Later renamed Nexus, Then came all kinds of browsers , until 1994 year , Netscape （Netscape） Released Navigator browser 0.9 edition , This is the first mature web browser in history , And then 1995 Microsoft launched IE browser , Since then, there has been a browser war , Microsoft adopts operating system bundling IE browser , Finally, we won an overwhelming victory , Losing the war Netscape Later acquired 、 Merge 、 dissolution . After a while IE Leading the way , And then be Opera,Safari,Firefox,Chrome Gradually carve up some market share , It has changed the situation of a dominant family .

But when it comes to JavaScript The history of , One company and one person must be mentioned , That's it Netscape The company and its employees Brendan Eich, Netscape released Navigator after , Eager to solve the problem of browser user interaction ,Javascript The father of Brendan Eich It only took 10 Days of time invented livescript( Why do we feel embarrassed ）, Because Netscape high-rise is java A fan of , Or to hold what was hot at that time java The thighs of ,livascript Renamed javascript,Brendan Eich His idea is ：
      （1） reference C The basic grammar of language ;

　　（2） reference Java Language data types and memory management ;

　　（3） reference Scheme Language , Raise the function to " First class citizens "（first class） The status of ;

　　（4） reference Self Language , Use prototype based （prototype） The inheritance mechanism of .
therefore ,Javascript Language is actually a mixture of two language styles ----（ A simplified ） Functional programming +（ A simplified ） object-oriented programming .
Javascript 1.0 Great success ,Netscape Then came the 1.1, After that, Microsoft, as a competitor, was at home IE3 Added the name JScript （ The name is different to avoid infringement ） Of JavaScript Realization . thus JavaScript The standardization of is put on the agenda ,1997 year , With JavaScript1.1 The proposal for the blueprint was submitted to European Association of computer manufacturers （ECMA）,ECMA After months of efforts, the leader has completed ECMA-262 —— It defines a type called ECMAScript The standard of the new scripting language .

although JavaScript and ECMAScript Usually used to express the same meaning , but JavaScript Compare the meaning of ECMA-262 There are so many rules in .
A complete JavaScript The implementation consists of three parts ：

（1） The core （ECMAScript）, Describes the syntax and basic objects of the language .

（2） Document object model （DOM）, Describe methods and interfaces for handling web content .

（3） Browser object model （BOM）, Describe the methods and interfaces for interacting with browsers .

1995 Invented in Javascript,1997 International standards were introduced in , There is an urgent need for browsers to interact with users ,javascript The development is too fast ,Javascript The specifications have not been adjusted yet , It solidifies . by comparison ,C Language is coming out 20 Years later, , International standards have just been issued .
Javascript There are many defects , however JavaScript Irreplaceable position in the front end ,

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