Detailed explanation of the three types of $() in jQuery-JS Tutorial-php.cn

Detailed explanation of the three types of $() in jQuery

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Release： 2018-04-20 09:08:59

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This time I will bring you a detailed explanation of the use of jQuery's three $()s. What are the precautions for the use of jQuery's three $()s. The following is a practical case, let's take a look.

$ is an alias for jQuery "class", and $() constructs a jQuery object. Therefore, "$()" can be called jQuery's constructor (personal opinion, haha!).

1. $() can be $(expresion), that is, css selector , Xpath or html element, that is, the target element is matched through the above expression.
For example: The object constructed by $("a") uses a CSS selector to construct a jQuery object - it selects all the tags. For example:
$("a").click(function(){...})
is the trigger event when any link on the page is clicked. To be precise, jQuery constructs an object $("a") using the tag , and the function click() is an (event) method of this jQuery object.
For example, there is such a piece of HTML code:

<p>one</p> 
<p> 
<p>two</p> 
</p> 
<p>three</p> 
<a href="#" id="test" onClick="jq()" >jQuery</a>

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The operation of this HTML is the following statement:

alert($("p>p").html());

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$() is a query expression, that is, using " A query expression such as p>p" constructs a jQuery object, and then "html()" means to display its html content, which is the [two] of the above HTML code snippet. Another example:

$("<p><p>Hello</p></p>").appendTo("body");

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$() contains a string. Use such a string to construct a jQuery object, and then add this string to .
2. $() can be $(element), which is a specific DOM element. For example, commonly used DOM objects include document, location, form, etc. For example, this line of code: The document in

$(document).find("p>p").html());

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$() is a DOM element, that is, it searches for the

element with

in the full text, and displays the content in

.
3. $() can be $(function), that is, a function, which is a shorthand for $(document).ready(). For example, the common form is like this:

$(document).ready(function(){ 
alert("Hello world!"); 
});

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Deformable operation:

$(function(){ 
alert("Hello world!"); 
});

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对于选择HTML文档中的elements，jQuery有两种方法：
1）如$("p>ul a")，它的意思是p标签中的ul标签中的a标签
不过，$('p>ul')和$('p ul')是有区别的，
$('p>ul')是

的直接后代里找

；
而$('p ul')是在

的所有后代里找

。
2）用jQuery对象的几个方法（如方法find()、each()等）
$("#orderedlist).find("li") 就像 $("#orderedlist li"). each()一样迭代了所有的li，而表达式中的“#”表示HTML中的ID，如上例中的“#orderedlist”就表示“ID为orderedlist所在的标签”。
****************************************************************
1、

标签选择器

类选择器

的直接后代里找

的所有后代里找

孩子节点，即使这个
的后代还有
也不是它所找的范围（所找到的DOM对象，只是它本级的DOM对象。）。而$('#sId li:not(.horizontal)')，就是指类名"sId"里面的所有li的子孙中没有horizontal类的所有元素。——这里的not()是一个negation pseudo class.
这里返回的是一个jQurey对象，一个数组对象，这个jQuery对象的长度可用.length()得到。
2、XPath选择器
如：选择所有带有title 属性的链接，我们会这样写：$('a[@title]')
[]里带@，说明[]里的是元素的属性；是个属性选择器
[]里没@，说明[]里的是元素的子孙。
$('ul li')和$('ul[li]')虽然返回的都是一个jQuery数组，但两者的含义正好相反。前者是要找
- 子孙，而后者却是在找所有子孙为
- 的