jQuery plug-in turns out to be so simple The mechanism and practice of jQuery plug-in

Types of jQuery plug-ins
1. Encapsulated object methods

This plug-in encapsulates object methods and is used to operate jQuery objects obtained through selectors. It is the most common plug-in. This type of plug-in can take advantage of the powerful advantages of jQuery selectors. A considerable number of jQuery methods are "inserted" into the kernel in this form within the jQuery script library, such as the parent() method and the appendTo() method. wait.

2. Encapsulate global functions

You can add independent functions to the jQuery namespace. For example, the commonly used jQuery.ajax() method and the jQuery.trim() method that removes leading and trailing spaces are all plugins attached to the kernel as global functions within jQuery.

3. Selector plug-in

Although jQuery’s selector is very powerful, in a few cases, you still need to use selector plug-ins to expand some of your favorite selectors.

The mechanism of jQuery plug-in
The mechanism of jQuery plug-in is very simple, which is to use the jQuery.fn.extend() and jQuery.extend() methods provided by jQuery to extend the functions of jQuery.

jQuery.fn.extend() is mostly used to extend the first of the three types mentioned above, and jQuery.extend() is used to extend the latter two plug-ins. Both methods accept one parameter, of type Object. The "name/value pairs" of the Object object respectively represent "function or method name/function body".

Some tips for writing jQuery plug-ins
1. It is recommended that the file name of the jQuery plug-in be named jquery.[plugin name].js to avoid confusion with other JS library plug-ins.

2. All object methods should be attached to the jQuery.fn object, and all global functions should be attached to the jQuery object itself.

3. Add a semicolon at the head of the plug-in to prevent other people’s irregular code from affecting the plug-in.

4. All methods or function plug-ins should end with a semicolon to avoid problems during compression

5. Unless the plug-in needs to return some variables that need to be obtained, the plug-in should return A jQuery object to ensure chainable operation of the plug-in.

6. It is helpful for the jQuery.extend() method to set the default parameters of the plug-in method and increase the usability of the plug-in.

jQuery plug-in structure
The jQuery plug-in structure is as follows:

Copy code The code is as follows:

 
;(function($){ 
/*Put the plug-in code here, you can use $ as an alias for jQuery*/ 
})(jQuery); 

encapsulation jQuery object method plug-in practical
Function: Set the color of the selected element, get the color of the first selected element

Naming: jquery.color.js

Structure:

Copy code The code is as follows:

 
;(function($){ 
$.fn.extend( { 
//Write the plug-in code here 
}); 
})(jQuery); 

Idea: Set a parameter value. If the parameter value is passed when calling, It is to set the color, otherwise it is to get the color. To get and set the color, you can use the css method provided by jQuery

Complete code:

Copy code The code is as follows :

 
;(function($){ 
$.fn.extend({ 
"color":function(value){ 
if(value==undefined){ 
return this.css("color"); 
} 
else{ 
return this.css("color",value); 
} 
} 
}) ; 
})(jQuery); 

Since the css() method has already determined the first element when getting the color, so here we directly use this.css("color") That’s it.

If it is a group of plug-ins, you can write it as follows:

Copy the code The code is as follows:

 
;(function($){ 
$.fn.extend({ 
"color":function(value){ 
//Plug-in code
}, 
" border":function(value){ 
//Plug-in code
}, 
"background":function(value){ 
//Plug-in code
} 
}); 
})(jQuery); 

Plug-in test: http://demo.jb51.net/js/2012/jquery_demo/encapsulating jQuery object method plug-in Demo.html
Practice of encapsulating global function plug-in
Function: Remove the left or right spaces individually

Name: jquery.lrtrim.js

Structure:

Copy code The code is as follows:

 
;(function($){ 
$.extend({ 
ltrim:function(text){ 
//Plug-in code
}, 
rtrim:function( text){ 
//Plug-in code
} 
}); 
})(jQuery); 

Idea: This type of plug-in is added inside the jQuery namespace For a function, just use regular expressions.

Complete code:

Copy code The code is as follows:

 
;(function ($){ 
$.extend({ 
ltrim:function(text){ 
return (text||"").replace(/^s /g,""); 
} , 
rtrim:function(text){ 
return (text||"").replace(/s $/g,""); 
} 
}); 
}) (jQuery); 

Plug-in test: http://demo.jb51.net/js/2012/jquery_demo/encapsulating global function jQuery plug-in Demo.html
Self Define selector plug-in in action
jQuery is known for its powerful selectors, so how does jQuery’s selector work?

jQuery’s selection parser first uses a set of regular expressions to parse the selector, and then executes a function, called the selection function, for each parsed selector. Finally, it is decided whether to retain the element based on whether the return value of the selection function is true or false, so that the matching element node can be found.

For example, $("div:gl(1)"), this selector will first obtain all

elements, then implicitly traverse these

elements, and select these < The ;div> element is used as a parameter, and some parameters such as "1" in parentheses are passed to the corresponding selector function of gt for judgment. If true is returned, it is retained, otherwise it is not retained. The result is a collection of

elements that meet the requirements.

The selector function accepts a total of 3 parameters, the form is as follows:

Copy code The code is as follows:

 
function (a,i,m){ 
//... 
} 

　The first parameter is a, which refers to the current traversal to DOM element.

The second parameter is i, which refers to the index value of the DOM element currently traversed, starting from 0.

The third parameter is m, which is the product of further parsing by the jQuery regular parsing engine. It is an array: the most important one is m[3], in $("div:gl(1 )") is the number "1" in parentheses.

There are already lt, gt and eq selectors in jQuery, so here is a selector between the two.

Function: Select elements with index values between a and b (a
Naming: jquery.between.js

Structure:

Copy code The code is as follows:

 
;(function($){ 
 $.extend($.expr[":"],{ 
between:function(a,i,m){ 
//Plug-in code
} 
}); 
}) (jQuery); 

Idea: Among the three parameters above, m[3] is in the form of "a, b", so separate m[3] with "," and then follow Compare the index value i, and return true if i is between the ranges represented by m[3], otherwise false

Complete code:

Copy Code The code is as follows:

 
;(function($){ 
$.extend($.expr[":"],{ 
between :function(a,i,m){ 
var temp=m[3].split(","); 
return temp[0]} 
}); 
})(jQuery); 

Note: temp[0] and temp[1] are used here to convert string numbers into numbers

Plug-in test: http://demo.jb51.net/js/2012/jquery_demo/jQuery custom selector plug-in DEMO.html
Summary
This article mainly introduces the jQuery plug-in Types, mechanisms, and actual combat for each type. I hope it can be helpful to everyone. I am also a beginner of jQuery, so everyone is welcome to try it out.

Reference book: "Sharp jQuery" (People's Posts and Telecommunications Publishing House)

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