occasionally , You want to have a function that can be used throughout the code . for example , You may want to have a single way to jQuery On the selector , Used to handle a series of operations on the selector . Or maybe you've written a very useful tool function , And hope to be able to simply migrate to other projects . under these circumstances , You may want to write a plug-in .

jQuery working principle 101:jQuery Object method and tool method

Before we write plug-ins , The first thing we need to do is jQuery I have some understanding of how . Take a look at this code :

 $( "a" ).css( "color", "red" );

This is a fairly basic jQuery Code , But do you know what's going on behind the scenes ? Whenever you use that $ Method to select an element , It returns a jQuery object . This object contains all the methods you've used (.css(), .click(), etc.) And all the elements that match the selector .jQuery Objects from $.fn Object to get these methods . This object contains all jQuery Object method , And if we want to write our own methods , It will also include these methods .

Besides ,jQuery Tool method $.trim() It is used to remove any leading or trailing white space characters from the user's input . Tool methods are those that reside directly in $ The method itself . When you expand jQuery API You don't have to worry about what you get back DOM When elements operate , You may want to write a tool method plug-in .

( The main idea of the original text is that $.trim() Method , And then explain it , But there's nothing on it $.trim(), So I have to do this .)

Basic plug-in writing

For example, we want to create a plug-in , Used to turn text in a set of retrieved elements green . All we need to do is add one called greenify The way to $.fn among , After that you will be able to use other jQuery Using it like the object method .

 $.fn.greenify = function() {
this.css( "color", "green" );
}; $( "a" ).greenify(); // Makes all the links green.

It should be noted that , Using another method .css() when , We used this instead of $(this) . It's because of our greenify Methods and .css() Belong to the same object .

Connective

The plug-in is ready to use , But we want our plug-in to be used in real combat , There are a few things we need to do . The serial is jQuery One of the characteristics of , It allows you to connect five or more operations on one selector . It's all done by putting all the jQuery Object method returns to the original jQuery Object ( But there are some exceptions : Call... Without parameters .width() Method returns the width of the selected element , And it can't be connected ). Let's use one line of code to make our plug-in method concatenate :

 $.fn.greenify = function() {
this.css( "color", "green" );
return this;
} $( "a" ).greenify().addClass( "greenified" );

Be careful , The concept of conjunction does not apply to jQuery Tool method , for example :$.trim().

Protect $Alias And add scope

stay JavaScript In the class library , $ Variables are very popular , If you are using jQuery At the same time using other class libraries , You may have to use jQuery.noConflict() Methods to make jQuery No longer use $ Variable . However , This will disrupt our plugins , Because it assumes $ yes jQuery In the case of alias . In order to be compatible with other plug-ins , And still use jQuery Of $ Alias , We need to put all the code in the function expression that we call immediately (Immediately Invoked Function Expression) among , And then transfer jQuery function , And will $ As a parameter :

 (function ( $ ) {
$.fn.greenify = function() {
this.css( "color", "green" );
return this;
}; $.ltrim = function( str ) {
return str.replace( /^\s+/, "" );
}; $.rtrim = function( str ) {
return str.replace( /\s+$/, "" );
}; }( jQuery ));

Besides , The main purpose of immediate function expressions is to allow us to have our own private variables . Suppose we need a different green color , And I want to store it in a variable .

 (function ( $ ) {
var shade = "#556b2f";
$.fn.greenify = function() {
this.css( "color", shade );
return this;
}; }( jQuery ));

Minimize plug-in footprint

When writing plug-ins , The best practice is to take only one $.fn Expansion slot . This reduces the chance that the plug-in will be covered , It also reduces the chance of covering other plug-ins . let me put it another way , The following is not appropriate :

 (function( $ ) {
$.fn.openPopup = function() {
// Open popup code.
}; $.fn.closePopup = function() {
// Close popup code.
}; }( jQuery ));

It is more reasonable to use only one expansion slot , Use parameters to control what the expansion slot does .

 (function( $ ) {
$.fn.popup = function( action ) {
if ( action === "open") {
// Open popup code.
} if ( action === "close" ) {
// Close popup code.
} }; }( jQuery ));

Use each() Method

The standard jQuery Object will contain any number of DOM Reference to element , That's why jQuery Objects are often treated as collections . If you want to do anything with a specific set of elements ( for example , Get one data attribute , Calculate specific properties, etc ) At this point you need to use .each() Method to traverse the set of elements .

 $.fn.myNewPlugin = function() {
return this.each(function() {
// Do something to each element here.
}); };

It should be noted that , We go back to .each() Method instead of returning this . because .each() The method is connectable , It will return this , And we go straight back this It's the same . This is the best practice we've done so far to stay connected .

Accept the option

As plug-ins get more and more complex , It's a good idea to make plug-ins customizable through options . Especially when there are many options , The simplest way is to use the literal amount of the object (object literal). Let's make some changes to the plug-in , Make it accept some options .

 (function ( $ ) {
$.fn.greenify = function( options ) {
// This is the easiest way to have default options.
var settings = $.extend({
// These are the defaults.
color: "#556b2f",
backgroundColor: "white"
}, options ); // Greenify the collection based on the settings variable.
return this.css({
color: settings.color,
backgroundColor: settings.backgroundColor
}); }; }( jQuery ));

Examples of use :

 $( "div" ).greenify({
color: "orange"
});

color The default value of #556b2f adopt $.extend() Method is covered , And it turns orange .

Complete implementation

Here is an example of a small plug-in , It uses some of the techniques we discussed earlier :

 (function( $ ) {
$.fn.showLinkLocation = function() {
return this.filter( "a" ).each(function() {
$( this ).append( " (" + $( this ).attr( "href" ) + ")" );
}); }; }( jQuery )); // Usage example:
$( "a" ).showLinkLocation();

This handy plug-in will traverse all anchors in the collection , And then href Attributes are appended to parentheses .

 <!-- Before plugin is called: -->
<a href="page.html">Foo</a> <!-- After plugin is called: -->
<a href="page.html">Foo (page.html)</a>

The plug-in can also be optimized as follows :

 (function( $ ) {
$.fn.showLinkLocation = function() {
return this.filter( "a" ).append(function() {
return " (" + this.href + ")";
}); }; }( jQuery ));

We will use .append() Method to accept a callback function , And the return value of the callback function depends on the content attached to each element in the collection . It should be noted that , At the same time, we didn't use .attr() How to get href attribute , Because of the original DOM API So that we can easily access the properly named href attribute .

Original address :http://learn.jquery.com/plugins/basic-plugin-creation/

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