What is the role of the $ symbol in jquery?

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

jQuery’s three kinds of $()

1. $() can be $(expresion), that is, css selector, Xpath or html element, that is, through The above expression to match the target element.

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("div>p").html());

$() is a DOM element, that is, it searches for the dc6dce4a544fdca2df29d5ac0ea9906b element with e388a4556c0f65e1904146cc1a846bee in the full text, and displays the content in e388a4556c0f65e1904146cc1a846bee.

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

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

Deformable operation:

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

The role of the $ symbol in jQuery

1. As a jQuery wrapper , use selectors to select DOM elements (this is also the most powerful function)

For example:

$("table tr:nth-child(even)")

2. Utility functions, as the namespace of several common utility functions Prefix

For example:

$.trim(someString)

3. Document ready handler, equivalent to $(document).ready(...)

For example:

$(function(){...}); //里面的函数会在DOM树加载完之后执行

4. Create DOM elements

For example:

$("<p>how are you?</p>")

5. Extend jQuery

For example:

$.fn.disable = function(){...}

6. Use jQuery and other libraries

For example: the Prototype library also uses the $ symbol. jQuery provides the noConflict function to avoid conflicts. jQuery.noConflict(); restores the $ symbol to the meaning defined by the non-jQuery library.

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