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JQuery Constructor
Advantages of JQuery
Small volume (v1.2.3 15kb)
Rich DOM selectors (CSS1-3 + XPath) across browsers (IE6, FF, Safari, Opera)
Blockchain chain code
◦ Powerful event and style support
◦ Powerful AJAX Functions
Extensions are easy to expand and many plug-ins are available.
JQuery constructor receives four types of parameters:
1. jQuery (expression, context)
2. jQuery (html)
3. jQuery (elements)
4. jQuery (fn)
First, find the elements in the document based on the expression (ID, DOM element name, CSS expression, and XPath expression), and assemble them into a jQuery object to return.
DEMO:
<! DOCTYPE html PUBLIC "-// W3C // dtd xhtml 1.0 Transitional // EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<Html xmlns = "http://www.w3.org/1999/xhtml">
<Head>
<Title> jQuery basic </title>
<Style type = "text/css">
. Selected
{
Background-color: Yellow;
}
</Style>
<Script src = "../scripts/jquery-1.2.3.intellisense.js" type = "text/javascript"> </script>
</Head>
<Body>
<H3> jQuery constructor <Ul>
<Li> jQuery (expression, context) </li>
<Li> jQuery (html) </li>
<Li> jQuery (elements) </li>
<Li> jQuery (fn) </li>
</Ul>
<Script type = "text/javascript">
</Script>
</Body>
</Html>
Add the following jQuery code to the script block at the end of the text:
JQuery ('ul> li: first '). addClass ("selected ");
JQuery () can be replaced with the shortcut $ (). If $ is occupied by other objects, you can use the jQuery. noConflict () function to cancel the shortcut.
In "ul> li: first", ul> li indicates all li elements under ul (CSS expressions, which can be ul/li in XPath mode). first indicates the first element. AddClass () is a function used by jQuery objects to add CSS style classes. The opposite function is removeClass ().
Add the following code:
$ ('Ul '). append ($ (' <li> new item </li> '));
$ ('<Li> new item </li>') converts the string to a DOM object, and adds it to the end of the ul object through the append () function.
Next:
$ (Document). ready (function (){
Watermarks ('ul').css ('color', 'red ');
});
The jQuery constructor can also pass in DOM objects, such as document or jQuery objects (of course it doesn't make any sense ). The ready () function adds an event handler for the document and sets the ul color to red.
$ (Document). ready () can be replaced directly with $ (fn) because of many application scenarios. fn indicates the processing function. (The ready processing function appears to be executed after the document content is loaded, and does not need to wait for other resources such as related images to be loaded, so it is executed earlier than the load event.
$ (Function (){
Alert ('Welcome to jQuery ');
});
The above code works as soon as the page is loaded, a dialog box is displayed.
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