📄 js_intro.asp
字号:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html lang="en-US" xml:lang="en-US" xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>JavaScript Introduction</title>
<link rel="shortcut icon" href="../favicon.ico" type="image/x-icon" />
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<meta name="Keywords" content="xml,tutorial,html,dhtml,css,xsl,xhtml,javascript,asp,ado,vbscript,dom,sql,colors,soap,php,authoring,programming,training,learning,beginner's guide,primer,lessons,school,howto,reference,examples,samples,source code,tags,demos,tips,links,FAQ,tag list,forms,frames,color table,w3c,cascading style sheets,active server pages,dynamic html,internet,database,development,Web building,Webmaster,html guide" />
<meta name="Description" content="Free HTML XHTML CSS JavaScript DHTML XML DOM XSL XSLT RSS AJAX ASP ADO PHP SQL tutorials, references, examples for web building." />
<meta http-equiv="pragma" content="no-cache" />
<meta http-equiv="cache-control" content="no-cache" />
<link rel="stylesheet" type="text/css" href="../stdtheme.css" />
<script type="text/javascript">
var gaJsHost = (("https:" == document.location.protocol) ? "../../https@ssl./default.htm" : "../../www./default.htm");
document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));
</script>
<script type="text/javascript">
var pageTracker = _gat._getTracker("UA-3855518-1");
pageTracker._initData();
pageTracker._trackPageview();
</script>
</head>
<body>
<a name="top"></a>
<table cellpadding="0" cellspacing="0" width="100%" bgcolor="#808080">
<tr>
<td width="234" valign="top">
<a href="../default.htm"><img src="../images/w3default80.jpg" border="0" alt="W3Schools" /></a>
</td>
<th valign="middle" align="left" class="right">
<script type="text/javascript"><!--
google_ad_client = "pub-3440800076797949";
/*txtimg*/
google_ad_slot = "5330033957";
google_ad_width = 728;
google_ad_height = 90;
//-->
</script>
<script type="text/javascript" src="../../pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
<noscript>
<a href="../default.asp" target="_blank"><img src="../banners/w6.gif" border="0" alt="W3Schools" /></a>
</noscript>
<br /></th>
</tr>
</table>
<table style="margin-left:1px" width="800px" border="0" cellpadding="0" cellspacing="2">
<tr>
<td width="137" class="content" valign="top"><br />
<a class="left" href="../default.asp" target="_top">
<img src="../images/homeicon.gif" border="0" alt="home" /></a>
<a class="left" href="../default.asp" target="_top">
<b>HOME</b></a>
<br /><br />
<b>JS Basic</b>
<br />
<a class="left" target="_top" href="default.asp" >JS HOME</a><br />
<a class="left" target="_top" href="js_intro.asp" style='font-weight:bold;'>JS Introduction</a><br />
<a class="left" target="_top" href="js_howto.asp" >JS How To</a><br />
<a class="left" target="_top" href="js_whereto.asp" >JS Where To</a><br />
<a class="left" target="_top" href="js_statements.asp" >JS Statements</a><br />
<a class="left" target="_top" href="js_comments.asp" >JS Comments</a><br />
<a class="left" target="_top" href="js_variables.asp" >JS Variables</a><br />
<a class="left" target="_top" href="js_operators.asp" >JS Operators</a><br />
<a class="left" target="_top" href="js_comparisons.asp" >JS Comparisons</a><br />
<a class="left" target="_top" href="js_if_else.asp" >JS If...Else</a><br />
<a class="left" target="_top" href="js_switch.asp" >JS Switch</a><br />
<a class="left" target="_top" href="js_popup.asp" >JS Popup Boxes</a><br />
<a class="left" target="_top" href="js_functions.asp" >JS Functions</a><br />
<a class="left" target="_top" href="js_loop_for.asp" >JS For Loop</a><br />
<a class="left" target="_top" href="js_loop_while.asp" >JS While Loop</a><br />
<a class="left" target="_top" href="js_break.asp" >JS Break Loops</a><br />
<a class="left" target="_top" href="js_loop_for_in.asp" >JS For...In</a><br />
<a class="left" target="_top" href="js_events.asp" >JS Events</a><br />
<a class="left" target="_top" href="js_try_catch.asp" >JS Try...Catch</a><br />
<a class="left" target="_top" href="js_throw.asp" >JS Throw</a><br />
<a class="left" target="_top" href="js_onerror.asp" >JS onerror</a><br />
<a class="left" target="_top" href="js_special_characters.asp" >JS Special Text</a><br />
<a class="left" target="_top" href="js_guidelines.asp" >JS Guidelines</a><br />
<br />
<b>JS Objects</b>
<br />
<a class="left" target="_top" href="js_obj_intro.asp" >JS Objects Intro</a><br />
<a class="left" target="_top" href="js_obj_string.asp" >JS String</a><br />
<a class="left" target="_top" href="js_obj_date.asp" >JS Date</a><br />
<a class="left" target="_top" href="js_obj_array.asp" >JS Array</a><br />
<a class="left" target="_top" href="js_obj_boolean.asp" >JS Boolean</a><br />
<a class="left" target="_top" href="js_obj_math.asp" >JS Math</a><br />
<a class="left" target="_top" href="js_obj_regexp.asp" >JS RegExp</a><br />
<a class="left" target="_top" href="js_obj_htmldom.asp" >JS HTML DOM</a><br />
<br />
<b>JS Advanced</b>
<br />
<a class="left" target="_top" href="js_browser.asp" >JS Browser</a><br />
<a class="left" target="_top" href="js_cookies.asp" >JS Cookies</a><br />
<a class="left" target="_top" href="js_form_validation.asp" >JS Validation</a><br />
<a class="left" target="_top" href="js_animation.asp" >JS Animation</a><br />
<a class="left" target="_top" href="js_image_maps.asp" >JS Image Maps</a><br />
<a class="left" target="_top" href="js_timing.asp" >JS Timing</a><br />
<a class="left" target="_top" href="js_objects.asp" >JS Create Object</a><br />
<a class="left" target="_top" href="js_summary.asp" >JS Summary</a><br />
<br />
<b>Examples/Quiz</b>
<br />
<a class="left" target="_top" href="js_examples.asp" >JS Examples</a><br />
<a class="left" target="_top" href="js_examples_2.asp" >JS Object Examples</a><br />
<a class="left" target="_top" href="js_examples_3.asp" >JS DOM Examples</a><br />
<a class="left" target="_top" href="js_quiz.asp" >JS Quiz</a><br />
<br />
<b>JS References</b>
<br />
<a class="left" target="_top" href="../jsref/default.asp" >JS Objects</a><br />
<a class="left" target="_top" href="../htmldom/dom_reference.asp" >JS HTML DOM</a><br />
<br />
<b>Selected Reading</b><br />
<a class="left" target="_top" href="../browsers/browsers_stats.asp">Web Statistics</a><br />
<a class="left" target="_top" href="../site/site_glossary.asp">Web Glossary</a><br />
<a class="left" target="_top" href="../hosting/default.asp">Web Hosting</a><br />
<a class="left" target="_top" href="../quality/default.asp">Web Quality</a><br /><br />
<a class="left" target="_top" href="../forum/default.asp">W3Schools Forum</a><br /><br />
<a class="left" target="_top" href="../about/about_helping.asp">Helping W3Schools</a><br /><br />
<script type="text/javascript"><!--
google_ad_client = "pub-3440800076797949";
/*LeftLinkUnit*/
google_ad_slot = "4854527104";
google_ad_width = 120;
google_ad_height = 90;
//-->
</script>
<script type="text/javascript"
src="../../pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
</td>
<td valign="top">
<table style="border: 1px solid gray" width="100%" bgcolor="#FFFFFF" border="0" cellpadding="5" cellspacing="0">
<tr>
<td>
<h1>Introduction to JavaScript</h1>
<a href="default.asp"><img border="0" alt="previous" src="../images/btn_previous.gif" width="100" height="20" /></a>
<a href="js_howto.asp"><img border="0" alt="next" src="../images/btn_next.gif" width="100" height="20" /></a>
<hr />
<p class="intro">JavaScript is used in millions of Web pages to improve the
design, validate forms, detect browsers, create cookies, and much more.</p>
<p class="intro">JavaScript is the most popular scripting language on the
internet, and works in all major browsers, such as Internet
Explorer, Mozilla, Firefox, Netscape, and Opera.</p>
<hr />
<h2>What You Should Already Know</h2>
<p>Before you continue you should have a basic understanding of the following:</p>
<ul>
<li>HTML / XHTML</li>
</ul>
<p>If you want to study these subjects first, find the tutorials on our
<a href="../default.asp">Home
page</a>.</p>
<hr />
<h2>What is JavaScript?</h2>
<ul>
<li>JavaScript was designed to add interactivity to HTML pages</li>
<li>JavaScript is a scripting language</li>
<li>A scripting language is a lightweight programming language</li>
<li>A JavaScript consists of lines of executable computer code</li>
<li>A JavaScript is usually embedded directly into HTML pages</li>
<li>JavaScript is an interpreted language (means that scripts execute without
preliminary compilation)</li>
<li>Everyone can use JavaScript without purchasing a
license</li>
</ul>
<hr />
<h2>Are Java and JavaScript the Same?</h2>
<p>NO!</p>
<p>Java and JavaScript are two completely different languages in both concept
and design!</p>
<p>Java (developed by Sun Microsystems) is a powerful and much more complex
programming language - in the same category as C and C++.</p>
<hr />
<h2>What can a JavaScript Do?</h2>
<ul>
<li><b>JavaScript gives HTML designers a programming tool - </b>HTML authors
are normally not programmers, but JavaScript is a scripting language with a
very simple syntax! Almost anyone can put small "snippets" of code into their
HTML pages</li>
<li><b>JavaScript can put dynamic text into an HTML page - </b>A JavaScript statement like this: document.write("<h1>" + name +
"</h1>") can write a variable text into an HTML page</li>
<li><b>JavaScript can react to events - </b>A JavaScript can be set to execute
when something happens, like when a page has finished loading or when a user
clicks on an HTML element</li>
<li><b>JavaScript can read and write HTML elements - </b>A JavaScript can read
and change the content of an HTML element</li>
<li><b>JavaScript can be used to validate data - </b>A JavaScript can be used
to validate form data before it is submitted to a server. This saves the
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -