Code examples of using JavaScript in HTML

This article mainly introduces the use of JavaScript example code in HTML. Friends who need it can refer to the

##3f1c4e4b6b16bbbd69b2ee476dc4f83a tag

In HTML5, script mainly has the following attributes: async, defer, charset, src, type,

• async (optional):

Keywords: asynchronous script, external file, immediate download;

When the tag contains this attribute, the script (external file) will be downloaded immediately. It is only valid for external script files. The page can be downloaded at the same time. For other operations, parsing and execution will stop after the download is completed, and parsing will continue after execution, but the execution order cannot be guaranteed.

<script src="js/index2.js" async="async"></script> 　

• #defer (optional):

Keywords: delay script, external file, delay Loading;

When the tag contains this attribute, the script can wait until the page is completely parsed or displayed before execution. It is only valid for external files. If there are two scripts with defer at the same time, due to delay , the former will be limited to the execution of the latter.

<script src="js/index1.js" defer="defer"></script>

• charset (optional):

Keywords: character set

Most browsers have ignored its value, so few people use it.

• src (optional):

Keywords: external reference

Represents the address of the external file that needs to be referenced.

• type (optional):

Keywords: MIME (scripting language content type)

To ensure maximum Compatible with limited browsers, the type attribute value is mainly text/javascript. If this attribute is not written, its default value is still text/javascript.

Note: When referencing external files, do not add other JS code to the tag. When parsing, the browser will only download the external script file referenced by src, and the code embedded in the table will be ignored. .

## 3f1c4e4b6b16bbbd69b2ee476dc4f83aLocation of tags Usually, we place tags with external files (including CSS files , JavaScript files) are placed in the same location, usually inside the 93f0f5c25f18dab9d176bd4f6de5d30e tag.

But once multiple JavaScript external files are encountered during the parsing process, the page cannot be fully displayed until all external files are loaded, so usually we will put it in the 6c04bd5ca3fcae76e30b72ad730ca86d tag at the bottom, as shown below:

As mentioned above, there is a defer attribute in 3f1c4e4b6b16bbbd69b2ee476dc4f83a, but since it is mentioned in HTML5, HTML5 will ignore it The defer attribute set by the embedded script is currently only supported by IE4~IE7. IE8 will fully follow the HTML5 standard from now on, so placing 3f1c4e4b6b16bbbd69b2ee476dc4f83a at the bottom of the 6c04bd5ca3fcae76e30b72ad730ca86d tag is still the best choice.

Advantages of referencing external files

#Easy to maintenance: putting all JavaScript files together not only It does not touch HTML code, and is more conducive to developers writing and maintaining code.
Accelerate browsing: If multiple HTML pages reference the same JavaScript external file, this file will only be loaded once (cached), which means that the page loading speed can be accelerated.
Safety: When referencing external files, if the user views the HTML code, they will not see the JavaScript code, which is more secure than writing it in a tag.

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##2b0b25ff593c5b6c03403dd6234ffb2ctag

Literally, NO-script, no script, that is The content in the 2b0b25ff593c5b6c03403dd6234ffb2c tag will only be displayed when the browser does not support JavaScript.

The browser does not support scripts;

• Browse The server supports scripts, but JavaScript is disabled;

• If any of the above two conditions is met, the content within the 2b0b25ff593c5b6c03403dd6234ffb2c tag will be displayed.

The page above gives the user a message, which will only be displayed when the browser does not support or disables JavaScript, otherwise the user will never see it and will not Will affect the display of other elements on the page.

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