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Introduction to JavaScript
JavaScript is a literal-translation scripting language, which is a dynamic type, a weak type, a prototype-based language, and a built-in support type. Its interpreter, known as the JavaScript engine, is widely used as a scripting language for the client, and is used in HTML (an application under the standard Universal Markup Language) to add dynamic functionality to an HTML Web page. Because JavaScript is compatible with the ECMA standard, it is also known as ECMAScript.
ECMAScript, describes the syntax and the basic object of the language's JavaScript composition .
The Document Object Model (DOM), which describes the methods and interfaces for working with Web page content.
A Browser object model (BOM) that describes the methods and interfaces that interact with the browser.
JavaScript Basic Features
1, is an explanatory scripting language (code is not precompiled)
2, mainly used to add interactive behavior to HTML (an application under standard Universal Markup Language) page
3, can be directly embedded HTML page, but written as a separate JS file conducive to the separation of structure and behavior
4, cross-platform features, under the support of most browsers, can be run on a variety of platforms (such as Windows, Linux, Mac, Android, iOS, etc.)
JavaScript uses
1. Scripts in HTML must be between <script> and </script> tags. The script can be placed in the <body> and <!DOCTYPE HTML><HTML> <Head> <MetaCharSet= "UTF-8"> <title>Document</title> <Script> //put JavaScript code here .Alert ("This is a test"); </Script> </Head> <Body> <Script> //put JavaScript code here .Alert ("This is a test"); </Script> </Body></HTML>2, JavaScript script can also be placed in the HTML external extension (. js) file (external script can not contain <script> tags), so as to better achieve the separation of behavior and structure.
<!DOCTYPE HTML><HTML> <Head> <MetaCharSet= "UTF-8"> <title>Document</title> </Head> <Body><!--introduce external JS files--<Scriptsrc= "Js/my.js"></Script> </Body></HTML>
3. JavaScript annotations
1 <script> 2 // single line comment 3 // document.createelement (" myelement "); 4 /* 5 multiline comment 6 Document.createelement ("myelement"); 7 document.createelement ("myelement"); 8 document.createelement ("myelement"); 9 */ 10 </script> 4. JavaScript statements and code blocks
Each JavaScript statement requires a semicolon (;) to end, and the procedure for omitting semicolons does not make an error, but a semicolon is generally required, with the following advantages:
1, improve code performance, if there is no semicolon parser need to analyze and determine where to insert a semicolon.
2, improve the correct rate of code, such as to write multiple lines of code on one line, there is no semicolon error is very likely.
JavaScript multiple statements are grouped together and placed in acurly braces ({})The statement block is formed within the//JavaScript Statementsvarx = 1;varx = 1; vary = 2;//writing multiple statements on one line is not recommended//JavaScript statement blocks, statement blocks can be nestedif(2 > 1) {x= 1; Y= 2; Z= 3; if(X <y) {z= 4; } if(X >y) {z= 5; }}
5. JavaScript case
JavaScript isstrictly case-sensitive, if the case is wrong, the program will error or not run properly. In a JavaScript program: JavaScript and JavaScript are completely different.First knowledge of JavaScript
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