Introduction to the location and function of the noscript element attribute in JavaScript

1. element attributes The main way to insert JavaScript into an XHTML page is to use the element. This element has 5 attributes: charset, defer, language, and src. , type, the three commonly used ones are type, src, and defer. 1. The value of the type attribute is generally text/javascript. This attribute is required, . 2. The value of the src attribute is an *.js external file. This attribute is optional, . In this example, the external file example.js will be loaded into the current page. The external file only needs to contain the Javascript code that would normally be placed between the opening and the closing . Just like parsing embedded Javascript code, page processing will also be temporarily stopped when parsing external Javascript files. It should be noted that with the src attribute, additional Javascript code should not be included between and . 3. The value of the defer attribute is "defer", which means that the script can be delayed until the document is completely parsed and displayed before execution. This attribute is optional, 2. Tag position According to convention, all elements should be placed in the element of the page, for example : Copy code The code is as follows: Modern web applications generally place all Javascript references in the element, placed after the content of the page The purpose is to make users feel that the page loads faster, as shown below: Copy code The code is as follows: 3. Delay script Use the defer attribute to delay the script. The purpose of this attribute is to indicate that the script will not affect the structure of the page when executed. That is, the script will be delayed until the entire page has been parsed. Copy code The code is as follows: In this example, although we put the element in the tag. 4. CDATA In XHTML (XML), the CData fragment is a special area in the document. This area can contain text content in any format that does not require parsing. Therefore, any characters can be used in the CData fragment without causing syntax errors. Copy code The code is as follows: // function compare(a,b){ if(a alert(“A is less than B”) ; }else if(a>b){ alert(“A is greater than B”) ; }else { alert(“A is equal to B”) ; } } //]]&gt ; Double slash comments are added to solve the problem of browser incompatibility with XHTML. 5. element When the browser does not support Javascript or Javascript is disabled, the elements contained in will be displayed. Otherwise, even if the page contains , but its content will not be displayed. As shown below: Copy the code The code is as follows: &lt ;/head> This page requires the browser to support (enable) Javascript.

This page will be displayed to the user if the script is invalid A message. In a script-enabled browser, the user will never see it - even though it is part of the page. Copy code The code is as follows: Example HTML Page This page requires the browser to support (enable) JavaScript

alert(1); Copy code The code is as follows: Example HTML Page This page requires the browser to support (enable) JavaScript

alert(1); In the following two cases, the content in the tag of the above code will be displayed: •The browser does not support scripts •Browse The server supports scripting, but scripting is disabled.

In addition, users will never see the content in the tag in the browser.

6. Summary To insert Javascript into XHTML, use the element. Use this element to embed Javascript into an XHTML page, mixing scripts with markup; you can also include external Javascript files. What we need to pay attention to are: 1. Both methods require that the value of the type attribute be set to text/javascript to indicate that the Javascript scripting language is used. 2. When including external Javascript files, the src attribute must be set to the url pointing to the corresponding file. This file can be a file located on the same server as the page containing it, or it can be a file in any other domain. 3. All elements will be parsed in order of their appearance on the page. The next code is parsed only after the previous code has been parsed. 4. The browser must first parse the code in the previous element before rendering the subsequent page content. For this reason, the element is generally placed at the end of the page, after the page content and before the closing tag. 5. In IE and Firefox, you can set the defer attribute to let the browser execute the script after rendering the document. Other browsers do not support this attribute. Alternatively, use the element to specify alternative content to be displayed in browsers that do not support scripts. However, when scripting is enabled, the browser will not display any content within the element.

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Introduction to the location and function of the noscript element attribute in JavaScript_javascript skills