The role of the $ symbol in jquery

The role of the $ symbol in jquery

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

   For example: $ ("Table tr:nth-child (even)")

2. Utility functions, as prefixes of namespaces for several common utility functions

   Example: $.trim (somestring)

3. The document-ready handler, which is equivalent to $ (documents). Prepare (...)

   For example: $ (function () {...}); The function inside will be executed after the DOM tree has been loaded.

4. Creating DOM elements

   For example: $ ("<p>how is you?</p>")

5. Extending jquery

   For example: $.fn.disable = function () {...}

6. Using jquery and other libraries

   For example: The prototype library is also using the $ sign, JQuery provides noconflict functions to avoid collisions, jquery.noconflict (); restore the $ symbol to the meaning of a non-jQuery library definition

7. JQuery Selector

Selector

Selector	Example	Select
*	$("*")	All elements
#ID	$ ("#lastname")	id= elements of "LastName"
. class	$ (". Intro")	All elements of class= "Intro"
Element	$ ("P")	All <p> elements
. class. class	$ (". Intro.demo")	All class= "Intro" and Class= "demo" Elements
: First	$ ("P:first")	First <p> Element
: Last	$ ("P:last")	Last <p> Element
: Even	$ ("Tr:even")	All even <tr> elements
: Odd	$ ("tr:odd")	All odd <tr> elements
: eq (index)	$ ("UL Li:eq (3)")	Fourth element in the list (index starting from 0)
: GT (no)	$ ("UL li:gt (3)")	List elements with index greater than 3
: LT (no)	$ ("UL Li:lt (3)")	List elements with index less than 3
: Not (selector)	$ ("Input:not (: Empty)")	All input elements that are not empty
: Header	$ (": Header")	All heading elements
: Animated		All animated elements
: Contains (text)	$ (": Contains (' W3school ')")	All elements containing the specified string
: Empty	$ (": Empty")	All elements with No child (element) nodes
: Hidden	$ ("P:hidden")	All hidden <p> elements
: Visible	$ ("table:visible")	All the visible tables
S1,s2,s3	$ ("Th,td,.intro")	All elements with a matching selection
[attribute]	$ ("[href]")	All elements with an HREF attribute
[attribute=value]	$ ("[href= ' # ']")	The value of all href attributes equals "#" elements
[attribute! =value]	$ ("[href!= ' # ']")	The value of all HREF attributes is not equal to the "#" element
[attribute$=value]	$ ("[href$= '. jpg ']")	The value of all HREF attributes contains elements ending with ". jpg"
: input	$ (": input")	All <input> elements
: Text	$ (": Text")	All <input> elements of type= "text"
:p Assword	$ (":p Assword")	All <input> elements of type= "password"
: Radio	$ (": Radio")	All <input> elements of type= "Radio"
: checkbox	$ (": checkbox")	All <input> elements of the type= "checkbox"
: Submit	$ (": Submit")	All <input> elements of type= "submit"
: RESET	$ (": Reset")	All <input> elements of type= "reset"
: button	$ (": Button")	All <input> elements of type= "button"
: Image	$ (": Image")	All <input> elements of type= "image"
: File	$ (": File")	All <input> elements of type= "file"
: Enabled	$ (": Enabled")	All the active input elements
:d isabled	$ (":d isabled")	All disabled input elements
: Selected	$ (": Selected")	All selected input elements
: Checked	$ (": Checked")	All selected input elements

The role of the $ symbol in jquery