JavaScript入门指南：互动网页编程的关键

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"这篇教程是关于JavaScript的基础介绍，适合初学者和有一定经验的开发者学习，旨在帮助读者理解和应用JavaScript来增强网页的交互性。作者Luka Abrus是微软克罗地亚的技术专家，他指出JavaScript在配合服务器端编程语言如ASP.NET时也发挥着重要作用。" JavaScript是一种广泛应用于网页开发的脚本语言，它的主要任务是为浏览器和网页添加动态交互功能。它能够与流行的服务器端编程语言和平台，如ASP.NET（在许多ASP.NET控件中使用JavaScript）紧密结合。由于学习曲线相对平缓，即使你是刚接触web开发的新手，也能快速上手编写自己的JavaScript脚本。在开始学习JavaScript之前，这个指南假设你已经具备了基本的HTML知识和对网页工作原理的理解。HTML虽然方便用于构建网页结构，但其静态的特性限制了它的表现力。例如，如果你希望在网页上显示当前日期，用HTML就无法实现，因为它不会根据时间变化而更新内容。这就是JavaScript发挥作用的地方。JavaScript是一种客户端脚本语言，它允许在用户浏览网页时动态改变内容。通过JavaScript，你可以实现如显示实时日期、响应用户输入、动画效果、表单验证等丰富多样的功能。这种动态性使得网页不再仅仅是静态的信息展示，而是可以与用户进行交互的平台。 JavaScript的核心概念包括变量、数据类型、控制流（如条件语句和循环）、函数以及对象。理解这些基本概念后，你就可以开始创建简单的脚本来改变网页的行为。随着技能的提升，还可以深入学习DOM（文档对象模型）操作，这将使你能够动态地创建、修改和删除网页的元素。此外，JavaScript还有许多库和框架，如jQuery、React和Vue.js，它们简化了JavaScript的开发，并提供了更高级的功能，如组件化和状态管理。了解并掌握这些工具，可以进一步提升你的web开发能力。 JavaScript是web开发不可或缺的一部分，无论你是想增强现有项目的用户体验，还是计划开发复杂的交互式应用，掌握JavaScript都将大大提升你的开发效率和作品质量。通过这个"JavaScript基础教程-绝对好"，你将踏上探索JavaScript世界的第一步，为你的网页开发生涯添加那个"额外的亮点"。

alert(text);

}

say("The page is loading!");

//-->

</script>

</head>

<body>

JavaScript is turned off.

</noscript>

<input type="button" value="Click me!" onclick="say('Thanks for

clicking!')" />

</body>

</html>

This example features a simple function. It takes a parameter and then displays it to the

user using alert method. The browser will read the page, read the function and store it

in memory and then read the JavaScript line that calls the function with parameter “The

page is loading!”. This line will call the function and show the text. All of this is

happening while the page is loading, and before the browser has read the rest of the

page. Here’s the result of this call:

After showing this message, the browser continues with reading the page. We’ve used a

NOSCRIPT element in the body of the page which is displayed only if JavaScript is

disabled or unavailable in the browser. Some users (to be more precise, around 4% of

them, as statistics show) intentionally turn JavaScript off and therefore JavaScript

scripts won’t run in their browsers. Inside of a NOSCRIPT element you can write a

message like “To fully experience this page, please turn on JavaScript” or something

similar.

The page also contains a simple button, but with a special attribute called onclick. This

attribute contains JavaScript code that will be run when the button is clicked (which is

rather logical, if you look at the attribute name). So when the user clicks on the button,

it will call our JavaScript function say with the text “Thanks for clicking!”.

Pay attention to the quotation marks used – the onclick attribute has its value inside of

double quotation marks. But to call the function say with a text parameter, we also must

use quotation marks, so we use single quotes to distinguish them from the onclick

attribute quotes.

Try this page out – while loading, the browser will display the text “The page is loading!”

and then load the rest of the page and display it. And then it will stop and wait. Nothing

will happen until you click the button. You can click the button as many times you like, it

will always display the message “Thanks for clicking!”.

Open up Visual Web Developer Express Edition, select File | New File | HTML Page and

copy the JavaScript above into this page.

You can also put another SCRIPT element at the end of the page and use it to call the

function say defined earlier on the page.

say("The page has almost loaded.");

</script>

You can also put all your JavaScript code in an external script. You can save all the code

without a SCRIPT element (just as pure JavaScript code) in a special file and then link it

to the page using SCRIPT element and its src attribute. For example, if you’ve put

JavaScript code in file called “myscript.js”, you could write:

</script>

This way your HTML page looks much clearer, and if you follow the practice of keeping

your CSS file separate from the HTML file, you can also do this with JavaScript code. In

addition, you can link this external JavaScript file to multiple, different pages. If you

create a function you want to use on several different pages, put it in an external

JavaScript file and link it to all those pages.

One of the downsides of client-side scripting is that all your visitors have access to the

source code of your scripts. With a simple View – Source in Internet Explorer, users can

access the complete source code of the page. As this source code also contains client-

side scripts (for the browser to execute), it’s easy to copy them. But when beginning

programming in JavaScript, that can be an advantage. If you spot some interesting

functionality on a page that you want to use on your own page, nothing is stopping you

from looking at the source code and analyzing the script.

We’ll look into functions, events and other topics shown so far with more details later in

this guide. Let’s start now with JavaScript basics.

Quiz 1

Question 1.1: Here are a few programming actions that are usually run on the server,

on the client or can be run on both. Check the appropriate boxes.

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JimMa

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