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Summary: The composition of JavaScript, the role of each component,
JavaScript is a scripting language designed to interact with Web pages, and its composition
| Javascript | ||
| ECMAScript (CORE) | DOM (Document Object model) | BOM (Browser object model) |
1.1ECMAScript
the Ecmascrip defined by ECMA-262 has no dependency on the Web browser, ECMA-262 defines only the basis of the language, providing core language functionality
ECMAScript is a standardized scripting language through ECMA-262, ECMA-262 language: syntax, type, statement, keyword, reserved word, operator, object
1.2 DOM (Document Object modle)
DOM is an application programming interface (Api,application programming Interface) for XML but extended for HTML, providing methods and interfaces for accessing and manipulating Web page content
The DOM maps the entire page to a multi-tiered node structure, and each component of the page, such as HTML or XML, is a node of a certain type, and these nodes contain different types of data.
1.3 BOM (Bower Object modle)
Controls the portion of the page that the browser displays, and the BOM only handles browser windows and frames, providing methods and interfaces for interacting with the browser
Second, <script> elements
2.1 referencing JavaScript files
<type= "Text/javascript" src= ": /.. /xx.js "></script>
<type= "Text/javascript">//javascript code </ Script >
The JavaScript code contained within the <script> element will be interpreted from top to bottom
2.2 Properties of the <script> element
<!DOCTYPE HTML><HTML> <Head> <Scripttype= "Text/javascript"defer= "Defer"src= "Example.js"></Script> </Head></HTML>
Although the <script> tag is within the
Same as defer only applies to externally introduced script files, Async tells the browser to download the file immediately, but unlike defer, it is not guaranteed that async scripts are executed in the order they are specified, and it is recommended that asynchronous scripts do not modify the DOM during loading
<!--Asynchronous Script -<Scripttype= "Text/javascript"Async= "Async"src= "Example1.js"></Script><Scripttype= "Text/javascript"Async= "Async"src= "Example2.js"></Script>
2.3 Properties of the <noscript> element
<!DOCTYPE HTML Public "-//W3C//DTD XHTML 1.0 transitional//en" "http://www.w3.org/TR/xhtml1/DTD/ Xhtml1-transitional.dtd "><HTMLxmlns= "http://www.w3.org/1999/xhtml"><Head><Metahttp-equiv= "Content-type"content= "text/html; charset=utf-8" /><title>Test</title><!--Delay Script -<ScriptType= "Text/javascript"defer= "Defer"src= "Example.js"></Script><!--Guide Script -<Scripttype= "Text/javascript"Async= "Async"src= "Example1.js"></Script><Scripttype= "Text/javascript"Async= "Async"src= "Example2.js"></Script></Head><Body> <NoScript> <P>This page shows the need for browser support (enabled) Javascript</NoScript></Body></HTML>
Learn JavaScript first from scratch (introduction)
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