jQuery使用小技巧

1.当document文档就绪时实施JavaScript代码。

俺们为何使用jQuery库呢?原因之一就在于大家得以使jQuery代码在种种分化的浏览器和存在bug的浏览器上完美运行。

<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。

运用&&操作符的特征是要是操作符左侧的表达式是false,那么它就不会再判断操作符右侧的表明式了。所以:

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

// You can write this:

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

4. is()方法比你想像的愈来愈有力。

上边举多少个例子,大家先写一个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!");

里面判断是或不是为动画本身认为那一个不错。

5.判定你的网页一共有多少元素。

通过行使$(“*”).length();方法可以判明网页的要素数量。

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

6.施用length()属性很笨重,上边大家使用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$()实际上是颇具三个参数的,你精通首个参数的机能吗?

// 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.施用jQuery大家得以判断一个链接是不是是外部的,并来添加一个icon在非外部链接中,且确定打开格局。

此处运用了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中的end()方法可以使你的jQuery链越发飞速。

<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.也许你指望你的web 应用感到更像原生的,那么您可以阻止contextmenu默许事件。

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

11.部分站点可能会使您的网页在一个bar上边,即我们所观看在上边的网页是iframe标签中的,大家得以这么化解。

// 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.你的内联样式表并不是被设置为不可改变的,如下:

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

如此即可改变内联样式了。

13.有时候我们不期待网页的某一局地情节被挑选比如复制粘贴那种工作,大家可以那样做:

<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>

如此那般,内容就不可能被挑选啊。

14.从CDN中引入jQuery,那样的办法可以坚实大家网站的特性,并且引入最新的版本也是一个没错的主张。

下边会介绍多种不相同的措施。

        <!-- 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.保障最小的DOM操作。

大家领悟js操作DOM是非常浪费资源的,大家得以看看下边的事例。

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.更便利的诠释URL。

兴许你会选拔正则表达式来解析URL,但那纯属不是一种好的艺术,大家能够借用a标签来促成它。

// 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.毫无惧怕使用vanilla.js。

jQuery背负的太多,那便是原因,你能够用一般的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.最优化你的选用器

// 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.缓存你的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.对于再度的函数只定义三回

万一你追求代码的更高品质,那么当您设置事件监听程序时务必小心,只定义一回函数然后把它的名字作为事件处理程序传递是不易的法门。

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

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

});

21.像对待数组一样地对待jQuery对象

鉴于jQuery对象有index值和尺寸,所以那意味着大家能够把对象当作普通的数组对待。那样也会有更好地性质。

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.当做复杂的修改时要分开元素。

修改一个dom元素要求网页重绘,这么些代价是慷慨激昂的,所以只要您想要再拉长质量,就足以品尝着当对一个因素举办大气改动时先从页面中分离那几个元素,修改完事后再添加到页面。

// 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.毫无平素等候load事件。

咱俩早就司空见惯了把大家拥有的代码都坐落ready的事件处理程序中,可是,即使您的html页面很巨大,decument
ready恐怕会被延缓了,所以对于部分大家不愿意ready后才方可接触的风浪能够置身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.当运用js给五个元素添加样式时更好的做法是创制一个style元素。

我们在此以前提到过,操作dom是相当慢的,所以当添加多个元素的体裁时制造一个style元素并添加到document中是更好的做法。

<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.给html元素分配一个名为JS的class。

当代的web
apps非凡的看重js,那里的一个技艺就是只有当js可用时才能显得特定的因素。看上边的代码。

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

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

如此那般,唯有js可用的时候id为message的要素才会突显;即使不辅助js,则该因素不会显得。

26.监听不设有的元素上的轩然大波。

jQuery拥有一个产业革命的事件处理机制,通过on()方法可以监听还不设有的风浪。
那是因为on方法可以传递一个元素的子元素拔取器作为参数。看下边的事例:

<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>');

那样,即便li是后创建的,也得以因此on()方法来监听。

27.只使用四回事件监听。

偶然,大家只要求绑定只运行两次的事件处理程序。那么one()方法是一个正确的选取,通过它你就足以高枕无忧了。

<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.效仿触发事件。

咱俩得以因而选拔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.应用触摸事件。

运用触摸事件和相关的鼠标事件并不曾太多分裂,不过你得有一个便于的位移装备来测试会更好。看上边那几个事例。

// 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.更好地利用on()/off()方法。

在jQuery1.7本卯时对事件处理进行了简化,看看上边的例子吗。

<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.更快地拦截默许事件表现。

咱俩驾驭js中可以运用preventDefault()方法来堵住默许行为,不过jQuery对此提供了更简单的办法。如下:

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

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

32.运用event.result链接多个事件处理程序。

对一个元素绑定四个事件处理程序并不广泛,而使用event.result更可以将三个事件处理程序联系起来。看上边的例证。

<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>

如此那般,控制台会输出Hip Hop!

33.创设你协调习惯的风浪。

您可以行使on()方法创造和谐喜爱的风云名称,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。

您知道如何在不下载一个文件的动静下通过发送一个ajax请求头获得一个文本的尺寸吗?
使用jQuery就很简单。

<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];
}

瞩目:这一个例子怎么样我们直接选拔浏览器是迫于获得的,必须运用当地的web服务器打开运行才得以。

35.运用延缓简化你的Ajax请求

延期(deferreds)是一个强有力的工具。jQuery对于每一个Ajax请求都会再次回到一个deferred对象。 deferred.done()艺术接受一个或多个参数,所有那一个都参数能够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。回调是根据他们添加的依次执行。一旦deferred.done()回来Deferred(延迟)对象,Deferred(延迟)可以链接其余的推迟对象,包罗扩展额外的.done()措施。下边那样就会使你的代码更易读:

// 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.平行的运作两个Ajax请求。

当我们必要发送三个Ajax请求是,相反于等待一个殡葬甘休再发送下一个,大家得以平行地发送来加速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

俺们不光可以在处理器上ping到一个网站的ip,也得以通过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.采取最简便易行的ajax请求

jQuery(使用ajax)提供了一个笔记的方法来火速下载内容并添加在一个要素中。

<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.种类化对象

jQuery提供了一个主意系列化表单值和一般的对象变成URL编码文本字符串。那样,大家就可以把系列化的值传给ajax()作为url的参数,轻松利用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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