jQuery使用小技巧

1.当document文档就绪时实施JavaScript代码。

俺们怎么以jQuery库呢?原因有即在我们可以使jQuery代码在各种不同之浏览器与在bug的浏览器上包罗万象运行。

<script src="http://code.jquery.com/jquery-1.10.2.min.js"></script>

        <script>

            // Different ways to achieve the Document Ready event

            // With jQuery
            $(document).ready(function(){ /* ... */});

            // Short jQuery
            $(function(){ /* ... */});

            // Without jQuery (doesn't work in older IE versions)
            document.addEventListener('DOMContentLoaded',function(){
                // Your code goes here
            });

            // The Trickshot (works everywhere):

            r(function(){
                alert('DOM Ready!');
            })

            function r(f){/in/.test(document.readyState)?setTimeout('r('+f+')',9):f()}

        </script>

2.使用route。

<script src="http://code.jquery.com/jquery-1.10.2.min.js"></script>

        <script>

            var route = {
                _routes : {},    // The routes will be stored here

                add    : function(url, action){
                    this._routes[url] = action;
                },

                run : function(){
                    jQuery.each(this._routes, function(pattern){
                        if(location.href.match(pattern)){
                            // "this" points to the function to be executed
                            this();
                        }
                    });
                }
            }

            // Will execute only on this page:
            route.add('002.html', function(){
                alert('Hello there!')
            });

            route.add('products.html', function(){
                alert("this won't be executed : (")
            });

            // You can even use regex-es:
            route.add('.*.html', function(){
                alert('This is using a regex!')
            });

            route.run();

        </script>

3.使用JavaScript中的AND技巧。

用&&操作符的特性是一旦操作符左边的表达式是false,那么它们就是不见面再也判断操作符右边的表达式了。所以:

// Instead of writing this:
if($('#elem').length){
    // do something
}

// You can write this:

$('#elem').length && log("doing something");

4. is()方法较你想象的逾有力。

下面举几独例子,我们事先勾勒一个id为elem的div。js代码如下:

// First, cache the element into a variable:
var elem = $('#elem');

// Is this a div?
elem.is('div') && log("it's a div");

// Does it have the bigbox class?
elem.is('.bigbox') && log("it has the bigbox class!");

// Is it visible? (we are hiding it in this example)
elem.is(':not(:visible)') && log("it is hidden!");

// Animating
elem.animate({'width':200},1);

// is it animated?
elem.is(':animated') && log("it is animated!");

里头判断是否为动画本身以为非常科学。

5.判断你的网页一共有略元素。

透过应用$(“*”).length();方法可判定网页的要素数量。

// How many elements does your page have?
log('This page has ' + $('*').length + ' elements!');

6.运length()属性很笨重,下面我们使用exist()方法。

/ Old way
log($('#elem').length == 1 ? "exists!" : "doesn't exist!");

// Trickshot:

jQuery.fn.exists = function(){ return this.length > 0; }

log($('#elem').exists() ? "exists!" : "doesn't exist!");

7.jQuery方法$()实际上是装有两个参数的,你懂得第二只参数的来意吗?

// Select an element. The second argument is context to limit the search
// You can use a selector, jQuery object or dom element

$('li','#firstList').each(function(){
    log($(this).html());
});

log('-----');

// Create an element. The second argument is an
// object with jQuery methods to be called

var div = $('<div>',{
    "class": "bigBlue",
    "css": {
        "background-color":"purple"
    },
    "width" : 20,
    "height": 20,
    "animate" : {   // You can use any jQuery method as a property!
        "width": 200,
        "height":50
    }
});

div.appendTo('#result');

8.应用jQuery我们得判定一个链接是否是外表的,并来上加一个icon在非外部链接中,且确定打开方式。

这里用了hostname属性。

<ul id="links"> 
   <li><a href="007.html">The previous tip</a></li> 
   <li><a href="./009.html">The next tip</a></li>
   <li><a href="http://www.google.com/">Google</a></li> 
</ul>

// Loop through all the links
$('#links a').each(function(){

    if(this.hostname != location.hostname){
        // The link is external
        $(this).append('<img src="assets/img/external.png" />')
               .attr('target','_blank');
    }

});

9.jQuery遭到之end()方法好要你的jQuery链更加迅速。

<ul id="meals"> <li> <ul class="breakfast"> <li class="eggs">No</li> <li class="toast">No</li> <li class="juice">No</li> </ul> </li> </ul>
// Here is how it is used:

var breakfast = $('#meals .breakfast');

breakfast.find('.eggs').text('Yes')
                      .end() // back to breakfast
                      .find('.toast').text('Yes')
                      .end()
                      .find('.juice').toggleClass('juice coffee').text('Yes');

breakfast.find('li').each(function(){
    log(this.className + ': ' + this.textContent)
});

10.或许你愿意您的web 应用感到又如原生的,那么您可以阻止contextmenu默认事件。

        <script>
            // Prevent right clicking on this page
            $(function(){
                $(document).on("contextmenu",function(e){
                    e.preventDefault();
                });
            });
        </script>

11.部分站点或会见要您的网页在一个bar下面,即我们所看到在底下的网页是iframe标签中之,我们可这样解决。

// Here is how it is used:

if(window != window.top){
    window.top.location = window.location;
}
else{
    alert('This page is not displayed in a frame. Open 011.html to see it in action.');
}

12.而的内联样式表并无是被装置为不可变更的,如下:

// Make the stylesheet visible and editable
$('#regular-style-block').css({'display':'block', 'white-space':'pre'})
                         .attr('contentEditable',true);

如此这般即可改变内联样式了。

13.产生时光我们无欲网页的有同部分内容让捎遵循复制粘贴这种事情,我们得以这样做:

<p class="descr">In certain situations you might want to prevent text on the page from being selectable. Try selecting this text and hit view source to see how it is done.</p>

     <script>
            // Prevent text from being selected
            $(function(){
                $('p.descr').attr('unselectable', 'on')
                           .css('user-select', 'none')
                           .on('selectstart', false);
          });
     </script>

诸如此类,内容就不可知给选哪。

14.于CDN中引入jQuery,这样的艺术可以增进我们网站的习性,并且引入最新的版也是一个对的意见。

脚会介绍四种植不同的主意。

        <!-- Case 1 - requesting jQuery from the official CDN -->
        <script src="http://code.jquery.com/jquery-1.10.2.min.js"></script>

        <!-- Case 2 - requesting jQuery from Google's CDN (notice the protocol) -->
        <!-- <script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script> -->

        <!-- Case 3 - requesting the latest minor 1.8.x version (only cached for an hour) -->
        <!-- <script src="//ajax.googleapis.com/ajax/libs/jquery/1.10/jquery.min.js"></script> -->

        <!-- Case 4 - requesting the absolute latest jQuery version (use with caution) -->
        <!-- <script src="http://code.jquery.com/jquery.min.js"></script> -->

15.保最好小的DOM操作。

咱们懂得js操作DOM是甚浪费资源的,我们可看下面的事例。

CODE
// Bad
//var elem = $('#elem');
//for(var i = 0; i < 100; i++){
//    elem.append('<li>element '+i+'</li>');
//}

// Good
var elem = $('#elem'),
    arr = [];

for(var i = 0; i < 100; i++){
    arr.push('<li>element '+i+'</li>');
}

elem.append(arr.join(''));

16.重便宜的说明URL。

可能你晤面下正则表达式来解析URL,但眼看纯属不是相同种植好之法子,我们得借用a标签来贯彻其。

// You want to parse this address into parts:
var url = 'http://tutorialzine.com/books/jquery-trickshots?trick=12#comments';

// The trickshot:
var a = $('<a>',{ href: url });

log('Host name: ' + a.prop('hostname'));
log('Path: ' + a.prop('pathname'));
log('Query: ' + a.prop('search'));
log('Protocol: ' + a.prop('protocol'));
log('Hash: ' + a.prop('hash'));

17.绝不惧怕使用vanilla.js。

jQuery背负的极端多,这就算是因,你得据此一般的js。

// Print the IDs of all LI items
$('#colors li').each(function(){

    // Access the ID directly, instead
    // of using jQuery's $(this).attr('id')

    log(this.id);

});

18.不过优化你的选择器

// Let's try some benchmarks!

var iterations = 10000, i;

timer('Fancy');

for(i=0; i < iterations; i++){
    // This falls back to a SLOW JavaScript dom traversal
    $('#peanutButter div:first');
}

timer_result('Fancy');

timer('Parent-child');

for(i=0; i < iterations; i++){
    // Better, but still slow
    $('#peanutButter div');
}

timer_result('Parent-child');

timer('Parent-child by class');

for(i=0; i < iterations; i++){
    // Some browsers are a bit faster on this one
    $('#peanutButter .jellyTime')

19.缓满怀你的selector。

// Bad:
// $('#pancakes li').eq(0).remove();
// $('#pancakes li').eq(1).remove();
// $('#pancakes li').eq(2).remove();

// Good:
var pancakes = $('#pancakes li');

pancakes.eq(0).remove();
pancakes.eq(1).remove();
pancakes.eq(2).remove();

// Alternatively:
// pancakes.eq(0).remove().end()
//           .eq(1).remove().end()
//           .eq(2).remove().end();

20.于再次的函数只定义一蹩脚

假定您追代码的又强性能,那么当您设置事件监听程序时务必小心,只定义一次函数然后把它们的名字作事件处理程序传递是毋庸置疑的法。

$(document).ready(function(){
    function showMenu(){
        alert('Showing menu!');
        // Doing something complex here
    }

    $('#menuButton').click(showMenu);
    $('#menuLink').click(showMenu);

});

21.像对待数组一样地比jQuery对象

由jQuery对象来index值和尺寸,所以就代表我们可拿目标当作普通的数组对待。这样呢会起重好地性。

var arr = $('li'),
    iterations = 100000;

timer('Native Loop');

for(var z=0;z<iterations;z++){

    var length = arr.length;
    for(var i=0; i < length; i++){
      arr[i];
    }
}
timer_result('Native Loop');

timer('jQuery Each');

for(z=0;z<iterations;z++){

    arr.each(function(i, val) {
      this;
    });
}
timer_result('jQuery Each');

22.看成复杂的改动时只要分别元素。

改一个dom元素要求网页重绘,这个代价是慷慨激昂的,所以要你想使又增长性,就足以品尝在当对一个要素进行大气改动时先期打页面中分离之因素,修改了之后再也上加到页面。

// Modifying in place
var elem = $('#elem');

timer('In place');

for(i=0; i &lt; iterations; i++){

    elem.width(Math.round(100*Math.random()));
    elem.height(Math.round(100*Math.random()));

}

timer_result('In place');

var parent = elem.parent();

// Detaching first
timer('Detached');

elem.detach();

for(i=0; i &lt; iterations; i++){

    elem.width(Math.round(100*Math.random()));
    elem.height(Math.round(100*Math.random()));

}

elem.appendTo(parent);

timer_result('Detached');

23.毫无一直守候load事件。

咱们曾习以为常了拿咱具备的代码都位居ready的事件处理程序中,但是,如果你的html页面很庞大,decument
ready恐怕会吃延缓了,所以于一些我们不期ready后才方可接触的轩然大波可以放在html的head元素中。

<script>

            // jQuery is loaded at this point. We can use
            // event delegation right away to bind events
            // even before $(document).ready:

            $(document).on('click', '#clickMe', function(){
                alert('Hit view source and see how this is made');
            });

            $(document).ready(function(){

                // This is where you would usually bind event handlers,
                // but as we are using delegation, there is no need to.

                // $('#clickMe').click(function(){ alert('Hey!'); });
            });

            // Note: You should place your script tags at the bottom of the page.
            // I have included them in the head only to demonstrate that we can bind
            // events before document ready and before the elements are created.

        </script>

24.当施用js给多个元素添加样式时还好的做法是创建一个style元素。

咱俩事先涉嫌过,操作dom是甚缓慢的,所以当上加多个要素的体裁时创造一个style元素并补充加至document中凡再次好的做法。

<ul id="testList">
 <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li> <li>Item</li>
 </ul>

var style = $('<style>');

// Try commenting out this line, or change the color:
style.text('#testList li{ color:red;}');

// Placing it before the result section so it affects the elements
style.prependTo('#result');

25.让html元素分配一个曰吧JS的class。

当代的web
apps非常之依赖js,这里的一个艺就是只有当js可用时才能够形特定的素。看下的代码。

$(document).ready(function(){
    $('html').addClass('JS');
});

  html.JS #message { display:block; }
 #message {display:none;}

如此这般,只有js可用的下id为message的素才见面显示;如果不支持js,则该因素不见面来得。

26.监放不设有的因素上之风波。

jQuery拥有一个先进的事件处理机制,通过on()方法可以监听还不存在的波。
这是为on方法可以传递一个因素的子元素选择器作为参数。看下的例证:

<ul id="testList"> <li>Old</li> <li>Old</li> <li>Old</li> <li>Old</li> </ul>

var list = $('#testList');

// Binding an event on the list, but listening for events on the li items:
list.on('click','li',function(){
    $(this).remove();
});

// This allows us to create li elements at a later time,
// while keeping the functionality in the event listener

list.append('<li>New item (click me!)</li>');

这么,即使li是继创造的,也可透过on()方法来监听。

27.只有行使同一次等事件监听。

偶然,我们惟有待绑定只运行一差的事件处理程序。那么one()方法是一个不利的抉择,通过它们你虽好高枕无忧了。

<button id="press">Press me!</ul>
var press = $('#press');

// There is a method that does exactly that, the one():
press.one('click',function(){
    alert('This alert will pop up only once');
});

// What this method does, is call on() behind the scenes,
// with a 1 as the last argument:
// press.on('click',null,null,function(){alert('I am the one and only!');}, 1);

28.拟触发事件。

咱得以经过以trigger模拟触发一个click事件。

<button id="press">Press me!</ul>
var press = $('#press');

// Just a regular event listener:
press.on('click',function(e, how){
    how = how || '';
    alert('The buton was clicked ' + how + '!');
});

// Trigger the click event
press.trigger('click');

// Trigger it with an argument
press.trigger('click',['fast']);

29.采用触摸事件。

采取触摸事件和有关的鼠标事件并无尽多不同,但是你得有一个利之位移装备来测试会再度好。看下面是事例。

// Define some variables
var ball = $('&lt;div id="ball"&gt;&lt;/div&gt;').appendTo('body'),
startPosition = {}, elementPosition = {};

// Listen for mouse and touch events
ball.on('mousedown touchstart',function(e){
    e.preventDefault();

    // Normalizing the touch event object
    e = (e.originalEvent.touches) ? e.originalEvent.touches[0] : e;

    // Recording current positions
    startPosition = {x: e.pageX, y: e.pageY};
    elementPosition = {x: ball.offset().left, y: ball.offset().top};

    // These event listeners will be removed later
    ball.on('mousemove.rem touchmove.rem',function(e){
        e = (e.originalEvent.touches) ? e.originalEvent.touches[0] : e;

        ball.css({
            top:elementPosition.y + (e.pageY - startPosition.y),
            left: elementPosition.x + (e.pageX - startPosition.x),
        });

    });
});

ball.on('mouseup touchend',function(){
    // Removing the heavy *move listeners
    ball.off('.rem');
});

30.重新好地用on()/off()方法。

在jQuery1.7本子时对事件处理进行了简化,看看下面的事例吧。

<div id="holder"> <button id="button1">1</button> <button id="button2">2</button> <button id="button3">3</button> <button id="button4">4</button> <button id="clear" style="float: right;">Clear</button> </div>

// Lets cache some selectors

var button1 = $('#button1'),
    button2 = $('#button2'),
    button3 = $('#button3'),
    button4 = $('#button4'),
    clear = $('#clear'),
    holder = $('#holder');

// Case 1: Direct event handling
button1.on('click',function(){
    log('Click');
});

// Case 2: Direct event handling of multiple events
button2.on('mouseenter mouseleave',function(){
    log('In/Out');
});

// Case 3: Data passing
button3.on('click', Math.round(Math.random()*20), function(e){

    // This will print the same number over and over again,
    // as the random number above is generated only once:
    log('Random number: ' + e.data);

});

// Case 4: Events with a namespace
button4.on('click.temp', function(e){
    log('Temp event!');
});

button2.on('click.temp', function(e){
    log('Temp event!');
});

// Case 5: Using event delegation
$('#holder').on('click', '#clear', function(){
    log.clear();
});

// Case 6: Passing an event map
var t; // timer

clear.on({

    'mousedown':function(){

        t = new Date();

    },

    'mouseup':function(){

        if(new Date() - t &gt; 1000){

            // The button has been held pressed
            // for more than a second. Turn off
            // the temp events

            $('button').off('.temp');
            alert('The .temp events were cleared!');
        }

    }
});

31.更快地阻挠默认事件作为。

咱们懂得js中好行使preventDefault()方法来遮默认行为,但是jQuery对这个提供了再也简短的措施。如下:

<a href="http://google.com/" id="goToGoogle">Go To Google</a>

$('#goToGoogle').click(false);

32.采取event.result链接多独事件处理程序。

针对一个要素绑定多只事件处理程序并无广,而动event.result更足以多单事件处理程序联系起。看下面的事例。

<button id="press">点击</button>
 <script src="http://code.jquery.com/jquery-1.10.2.min.js"></script>
 <script>

var press = $('#press');
press.on('click',function(){
    return 'Hip';
});

// The second event listener has access
// to what was returned from the first

press.on('click',function(e){
    console.log(e.result + ' Hop!');
});
 </script>

然,控制台会输出Hip Hop!

33.创办而协调习惯的风波。

乃可采取on()方法创建和谐喜欢的风波名称,然后经过trigger来触发。举例如下:

<button id="button1">Jump</button> <button id="button2">Punch</button> <button id="button3">Click</button> <button id="clear" style="float: right;">Clear</button> <div id="eventDiv"></div>
     <script src="http://code.jquery.com/jquery-1.10.2.min.js"></script>

     <script>

var button1 = $('#button1'),
    button2 = $('#button2'),
    button3 = $('#button3'),
    clear = $('#clear'),
    div = $('#eventDiv');

div.on({
    jump : function(){
        alert('Jumped!');
    },

    punch : function(e,data){
        alert('Punched '+data+'!');
    },

    click : function(){
        alert('Simulated click!');
    }

});

button1.click(function(){
    div.trigger('jump');
});

button2.click(function(){
    // Pass data along with the event
    div.trigger('punch',['hard']);
});

button3.click(function(){
    div.trigger('click');
});

clear.click(function(){
    //some clear code
});

     </script>

34.在下载文件旁显示文件大小。

汝了解怎么样当未生充斥一个文本的状下通过发送一个ajax请求头得到一个文书的轻重缓急也?
使用jQuery就生容易。

<a href="001.html" class="fetchSize">First Trickshot</a> <br /> 
<a href="034.html" class="fetchSize">This Trickshot</a> <br /> 
<a href="assets/img/ball.png" class="fetchSize">Ball.png</a> <br />

// Loop all .fetchSize links
$('a.fetchSize').each(function(){

    // Issue an AJAX HEAD request for each one
    var link = this;

    $.ajax({
        type        : 'HEAD',
        url            : link.href,
        complete    : function(xhr){

            // Append the filesize to each
            $(link).append(' (' + humanize(xhr.getResponseHeader('Content-Length')) + ')');

        }
    });

});

function humanize(size){
    var units = ['bytes','KB','MB','GB','TB','PB'];

    var ord = Math.floor( Math.log(size) / Math.log(1024) );
    ord = Math.min( Math.max(0,ord), units.length-1);

    var s = Math.round((size / Math.pow(1024,ord))*100)/100;
    return s + ' ' + units[ord];
}

留意:这个事例如何我们一直运用浏览器是迫不得已得到的,必须采取当地的web服务器打开运行才可。

35.应用延缓简化你的Ajax请求

缓(deferreds)是一个雄的家伙。jQuery对于各一个Ajax请求都见面回去一个deferred对象。 deferred.done()方式接受一个或者多只参数,所有这些还参数可以是一个单一的函数或一个函数数组。当Deferred(延迟)解决时,doneCallbacks被调用。回调是按照他们添加的依次执行。一旦deferred.done()返Deferred(延迟)对象,Deferred(延迟)可以链接其它的推移对象,包括多额外的.done()主意。下面这样虽会见使你的代码更易读:

// This is equivalent to passing a callback as the
// second argument (executed on success):

$.get('assets/misc/1.json').done(function(r){
    log(r.message);
});

// Requesting a file that does not exist. This will trigger
// the failure response. To handle it, you would normally have to
// use the full $.ajax method and pass it as a failure callback,
// but with deferreds you can can simply use the fail method:

$.get('assets/misc/non-existing.json').fail(function(r){
    log('Oops! The second ajax request was "' + r.statusText + '" (error ' + r.status + ')!');
});

36.平的运作多个Ajax请求。

当我们要发送多独Ajax请求是,相反于等一个殡葬完再发送下一个,我们可以平行地发送来加快Ajax请求发送。

// The trick is in the $.when() function:

$.when($.get('assets/misc/1.json'), $.get('assets/misc/2.json')).then(function(r1, r2){
    log(r1[0].message + " " + r2[0].message);
});

37.通过jQuery获得ip

俺们不光可于电脑及ping到一个网站的ip,也可经过jQuery得到。

$.get('http://jsonip.com/', function(r){ log(r.ip); });

// For older browsers, which don't support CORS
// $.getJSON('http://jsonip.com/?callback=?', function(r){ log(r.ip); });

38.下最简便的ajax请求

jQuery(使用ajax)提供了一个记的法子来快速下载内容连补充加在一个素中。

<p class="content"></p> <p class="content"></p>

var contentDivs = $('.content');

// Fetch the contents of a text file:
contentDivs.eq(0).load('1.txt');

// Fetch the contents of a HTML file, and display a specific element:
contentDivs.eq(1).load('1.html #header');

39.序列化对象

jQuery提供了一个方式序列化表单值和一般的对象变成URL编码文本字符串。这样,我们就足以管序列化的值传给ajax()作为url的参数,轻松使用ajax()提交表单了。

<form action="">
First name: <input type="text" name="FirstName" value="Bill" /><br />
Last name: <input type="text" name="LastName" value="Gates" /><br />
</form>

// Turn all form fields into a URL friendly key/value string.
// This can be passed as argument of AJAX requests, or URLs.

$(document).ready(function(){
    console.log($("form").serialize()); // FirstName=Bill&LastName=Gates
});

// You can also encode your own objects with the $.param method:
log($.param({'pet':'cat', 'name':'snowbell'}));

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