JavaScript

<script> tag

The <script> tag is used to define a script (JavaScript).

The <script> element either contains scripting statements or it points to an external script file through the src attribute.

Common uses for JavaScript are image manipulation, form validation, and dynamic changes of content.

<script>
document.getElementById("demo").innerHTML = "Hello JavaScript!";
</script>

Writes Hello JavaScript! into an HTML element with id="demo"

<noscript> tag

The <noscript> tag is used to provide an alternate content for users that have disabled scripts in their browser or have a browser that doesn't support client-side scripting. (不支持Javascript的浏览器需要使用)

The <noscript> element can contain all the elements that you can find inside the <body> element of a normal HTML page.

The content inside the <noscript> element will only be displayed if scripts are not supported, or are disabled in the user's browser:

<script>
document.getElementById("demo").innerHTML = "Hello JavaScript!";
</script>

<noscript>Sorry, your browser does not support JavaScript!</noscript>

Taste of JavaScript

JavaScript can change HTML content:

document.getElementById("demo").innerHTML = "Hello JavaScript!";

JavaScript can change HTML styles:

document.getElementById("demo").style.fontSize = "25px";

JavaScript can change HTML attributes:

document.getElementById("image").src = "picture.gif";

Script tags

Tag Description
<script> Defines a client-side script
<noscript> Defines an alternate content for users that do not support client-side scripts