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JavaScript jQuery 规范

发布于 2017-07-22 字数7716 浏览 1151 评论 0

使用最新版本的 jQuery

最新版本的 jQuery 会改进性能和增加新功能,若不是为了兼容旧浏览器,建议使用最新版本的 jQuery。以下是三条常见的 jQuery 语句,版本越新,性能越好:

$('.elem')
$('.elem', context)
context.find('.elem')

JavaScript jQuery 规范

分别使用 1.4.2、1.4.4、1.6.2 三个版本测试浏览器在一秒内能够执行多少次,结果 1.6.2 版执行次数远超两个老版本。

jQuery 变量

  1. 存放 jQuery 对象的变量以 $ 开头;
  2. 将 jQuery 选择器返回的对象缓存到本地变量中复用;
  3. 使用驼峰命名变量;
var $myDiv = $("#myDiv");
$myDiv.click(function(){...});

选择器

  1. 尽可能的使用 ID 选择器,因为它会调用浏览器原生方法 document.getElementById 查找元素。当然直接使用原生 document.getElementById 方法性能会更好;
  2. 在父元素中选择子元素使用 .find() 方法性能会更好, 因为 ID 选择器没有使用到 Sizzle 选择器引擎来查找元素;
// Not recommended
var $productIds = $("#products .class");

// Recommended
var $productIds = $("#products").find(".class");

DOM 操作

  1. 当要操作 DOM 元素的时候,尽量将其分离节点,操作结束后,再插入节点;
  2. 使用字符串连接或 array.join 要比 .append()性能更好;
var $myList = $("#list-container > ul").detach();
//...a lot of complicated things on $myList
$myList.appendTo("#list-container");
// Not recommended
var $myList = $("#list");
for(var i = 0; i < 10000; i++){
    $myList.append("<li>"+i+"</li>");
}

// Recommended
var $myList = $("#list");
var list = "";
for(var i = 0; i < 10000; i++){
    list += "<li>"+i+"</li>";
}
$myList.html(list);

// Much to recommended
var array = [];
for(var i = 0; i < 10000; i++){
    array[i] = "<li>"+i+"</li>";
}
$myList.html(array.join(''));

事件

  1. 如果需要,对事件使用自定义的 namespace,这样容易解绑特定的事件,而不会影响到此 DOM 元素的其他事件监听;
  2. 对 Ajax 加载的 DOM 元素绑定事件时尽量使用事件委托。事件委托允许在父元素绑定事件,子代元素可以响应事件,也包括 Ajax 加载后添加的子代元素;
$("#myLink").on("click.mySpecialClick", myEventHandler);
$("#myLink").unbind("click.mySpecialClick");
// Not recommended
$("#list a").on("click", myClickHandler);

// Recommended
$("#list").on("click", "a", myClickHandler);

链式写法

  1. 尽量使用链式写法而不是用变量缓存或者多次调用选择器方法;
  2. 当链式写法超过三次或者因为事件绑定变得复杂后,使用换行和缩进保持代码可读性;
$("#myDiv").addClass("error").show();
$("#myLink")
  .addClass("bold")
  .on("click", myClickHandler)
  .on("mouseover", myMouseOverHandler)
  .show();

其他

  1. 多个参数使用对象字面量存储;
  2. 不要将 CSS 写在 jQuery 里面;
  3. 正则表达式仅准用 .test() 和 .exec() 。不准用 “string”.match() ;

jQuery 插件模板

// jQuery Plugin Boilerplate
// A boilerplate for jumpstarting jQuery plugins development
// version 1.1, May 14th, 2011
// by Stefan Gabos

// remember to change every instance of "pluginName" to the name of your plugin!
(function($) {

    // here we go!
    $.pluginName = function(element, options) {

        // plugin's default options
        // this is private property and is  accessible only from inside the plugin
        var defaults = {

            foo: 'bar',

            // if your plugin is event-driven, you may provide callback capabilities
            // for its events. execute these functions before or after events of your
            // plugin, so that users may customize those particular events without
            // changing the plugin's code
            onFoo: function() {}

        }

        // to avoid confusions, use "plugin" to reference the
        // current instance of the object
        var plugin = this;

        // this will hold the merged default, and user-provided options
        // plugin's properties will be available through this object like:
        // plugin.settings.propertyName from inside the plugin or
        // element.data('pluginName').settings.propertyName from outside the plugin,
        // where "element" is the element the plugin is attached to;
        plugin.settings = {}

        var $element = $(element), // reference to the jQuery version of DOM element
             element = element;    // reference to the actual DOM element

        // the "constructor" method that gets called when the object is created
        plugin.init = function() {

            // the plugin's final properties are the merged default and
            // user-provided options (if any)
            plugin.settings = $.extend({}, defaults, options);

            // code goes here

        }

        // public methods
        // these methods can be called like:
        // plugin.methodName(arg1, arg2, ... argn) from inside the plugin or
        // element.data('pluginName').publicMethod(arg1, arg2, ... argn) from outside
        // the plugin, where "element" is the element the plugin is attached to;

        // a public method. for demonstration purposes only - remove it!
        plugin.foo_public_method = function() {

            // code goes here

        }

        // private methods
        // these methods can be called only from inside the plugin like:
        // methodName(arg1, arg2, ... argn)

        // a private method. for demonstration purposes only - remove it!
        var foo_private_method = function() {

            // code goes here

        }

        // fire up the plugin!
        // call the "constructor" method
        plugin.init();

    }

    // add the plugin to the jQuery.fn object
    $.fn.pluginName = function(options) {

        // iterate through the DOM elements we are attaching the plugin to
        return this.each(function() {

            // if plugin has not already been attached to the element
            if (undefined == $(this).data('pluginName')) {

                // create a new instance of the plugin
                // pass the DOM element and the user-provided options as arguments
                var plugin = new $.pluginName(this, options);

                // in the jQuery version of the element
                // store a reference to the plugin object
                // you can later access the plugin and its methods and properties like
                // element.data('pluginName').publicMethod(arg1, arg2, ... argn) or
                // element.data('pluginName').settings.propertyName
                $(this).data('pluginName', plugin);

            }

        });

    }

})(jQuery);

此 jQuery 插件模板出自:jQuery Plugin Boilerplate, revisited

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