【译】jQuery的50个使用技巧

时间 2019-11-17

标签 jquery 使用技巧栏目 JQuery 繁體版

原文原文链接

1.当document文档就绪时执行JavaScript代码。

<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> 复制代码

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>
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3.使用JavaScript中的AND技巧。

使用&&操做符的特色是若是操做符左边的表达式是false，那么它就不会再判断操做符右边的表达式了。因此：php

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

// You can write this:

$('#elem').length && log("doing something");
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4. is()方法比你想象的更为强大。

下面举几个例子，咱们先写一个id为elem的div。js代码以下：css

// 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!");
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其中判断是否为动画我以为很是不错。html

5.判断你的网页一共有多少元素。

经过使用$("*").length属性能够判断网页的元素数量。jquery

// How many elements does your page have?
log('This page has ' + $('*').length + ' elements!');
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6.使用length()属性很笨重，下面咱们使用exist()方法。

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

// Trickshot:

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

log($('#elem').exists() ? "exists!" : "doesn't exist!");
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7.jQuery方法$()其实是拥有两个参数的，你知道第二个参数的做用吗？

// 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');
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8.使用jQuery咱们能够判断一个连接是不是外部的，并来添加一个icon在非外部连接中，且肯定打开方式。

这里用到了hostname属性。c++

<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');
    }

});
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9.jQuery中的end()方法可使你的jQuery链更加高效。

<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)
});
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10.也许你但愿你的web 应用感受更像原生的，那么你能够阻止contextmenu默认事件。

<script>
    // Prevent right clicking on this page
    $(function(){
        $(document).on("contextmenu",function(e){
            e.preventDefault();
        });
    });
</script>
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11.一些站点可能会使你的网页在一个bar下面，即咱们所看到在下面的网页是iframe标签中的，咱们能够这样解决。

// 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.');
}
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12.你的内联样式表并非被设置为不可改变的，以下：

// Make the stylesheet visible and editable
$('#regular-style-block').css({'display':'block', 'white-space':'pre'})
                         .attr('contentEditable',true);
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这样便可改变内联样式了。web

13.有时候咱们不但愿网页的某一部份内容被选择好比复制粘贴这种事情，咱们能够这么作：ajax

<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>
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这样，内容就不能被选择啦。正则表达式

14.从CDN中引入jQuery，这样的方法能够提升咱们网站的性能，而且引入最新的版本也是一个不错的主意。

下面会介绍四种不一样的方法。json

<!-- 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> --> 复制代码

15.保证最小的DOM操做。

咱们知道js操做DOM是很是浪费资源的，咱们能够看看下面的例子。api

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(''));
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16.更方便的分解URL。

也许你会使用正则表达式来解析URL，但这绝对不是一种好的方法，咱们能够借用a标签来实现它。

// 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'));
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17.不要惧怕使用vanilla.js。

jQuery背负的太多，这即是缘由，你能够用通常的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); }); 复制代码

18.最优化你的选择器

// 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')
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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();
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20.对于重复的函数只定义一次

若是你追求代码的更高性能，那么当你设置事件监听程序时必须当心，只定义一次函数而后把它的名字做为事件处理程序传递是不错的方法。

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

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

});
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21.像对待数组同样地对待jQuery对象

因为jQuery对象有index值和长度，因此这意味着咱们能够把对象看成普通的数组对待。这样也会有更好地性能。

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');
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22.当作复杂的修改时要分离元素。

修改一个dom元素要求网页重绘，这个代价是高昂的，因此若是你想要再提升性能，就能够尝试着当对一个元素进行大量修改时先从页面中分离这个元素，修改完以后再添加到页面。

// 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');
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23.不要一直等待load事件。

咱们已经习惯了把咱们全部的代码都放在ready的事件处理程序中，可是，若是你的html页面很庞大，decument ready恐怕会被延迟了，因此对于一些咱们不但愿ready后才能够触发的事件能够放在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>
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24.当使用js给多个元素添加样式时更好的作法是建立一个style元素。

咱们以前提到过，操做dom是很是慢的，因此当添加多个元素的样式时建立一个style元素并添加到document中是更好的作法。

<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');
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25.给html元素分配一个名为JS的class。

现代的web apps很是的依赖js，这里的一个技巧就是只有当js可用时才能显示特定的元素。看下面的代码。

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


html.JS #message { display:block; }
#message {display:none;}
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这样，只有js可用的时候id为message的元素才会显示；若是不支持js，则该元素不会显示。

26.监听不存在的元素上的事件。

jQuery拥有一个先进的事件处理机制，经过on()方法能够监听还不存在的事件。这是由于on方法能够传递一个元素的子元素选择器做为参数。看下面的例子：

<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>');
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这样，即便li是后建立的，也能够经过on()方法来监听。

27.只使用一次事件监听。

有时，咱们只须要绑定只运行一次的事件处理程序。那么one()方法是一个不错的选择，经过它你就能够高枕无忧了。

<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);
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28.模拟触发事件。

咱们能够经过使用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']);
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29.使用触摸事件。

使用触摸事件和相关的鼠标事件并无太多不一样，可是你得有一个方便的移动设备来测试会更好。看下面这个例子。

// 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');
});
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30.更好地使用on()/off()方法。

在jQuery1.7版本时对事件处理进行了简化，看看下面的例子吧。

<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!');
        }

    }
});
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31.更快地阻止默认事件行为。

咱们知道js中可使用preventDefault()方法来阻止默认行为，可是jQuery对此提供了更简单的方法。以下：

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

$('#goToGoogle').click(false);
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32.使用event.result连接多个事件处理程序。

对一个元素绑定多个事件处理程序并不常见，而使用event.result更能够将多个事件处理程序联系起来。看下面的例子。

<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>
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这样，控制台会输出Hip Hop!

33.建立你本身习惯的事件。

你可使用on()方法建立本身喜欢的事件名称，而后经过trigger来触发。举例以下：

<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>
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34.在下载文件旁显示文件大小。

你知道如何在不下载一个文件的状况下经过发送一个ajax请求头获得一个文件的大小吗？使用jQuery就很容易。

<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];
}
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注意：这个例子如何咱们直接使用浏览器是无法获得的，必须使用本地的web服务器打开运行才能够。

35.使用延迟简化你的Ajax请求

延迟(deferreds)是一个强大的工具。jQuery对于每个Ajax请求都会返回一个deferred对象。 deferred.done()方法接受一个或多个参数，全部这些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。回调是依照他们添加的顺序执行。一旦deferred.done()返回Deferred（延迟）对象，Deferred（延迟）能够连接其它的延迟对象，包括增长额外的.done()方法。下面这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 + ')!');
});
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36.平行的运行多个Ajax请求。

当咱们须要发送多个Ajax请求是，相反于等待一个发送结束再发送下一个，咱们能够平行地发送来加速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);
});
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37.经过jQuery得到ip

咱们不只能够在电脑上ping到一个网站的ip，也能够经过jQuery获得。

$.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); }); 复制代码

38.使用最简单的ajax请求

jQuery（使用ajax）提供了一个速记的方法来快速下载内容并添加在一个元素中。

<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');
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39.序列化对象

jQuery提供了一个方法序列化表单值和通常的对象成为URL编码文本字符串。这样，咱们就能够把序列化的值传给ajax()做为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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40.使用jQuery上传二进制文件

如今的浏览器都支持FormData API，这能够是咱们很轻松的经过ajax来发送数据。并将之结合HTML5中的File API，咱们就能够上传二进制文件了。

// The file input field

var fileInput = $('input[type=file]'),
    button = $('#upload');

button.on('click', function(){

    // Access the files property, which holds
    // an array with the selected files

    var files = fileInput.prop('files');

    // No file was chosen!
    if(files.length == 0) {
        alert('Please choose a file to upload!');
        return false;
    }

    // Create a new FormData object

    var fd = new FormData();

    fd.append('file', files[0]);

    // Upload the file to assets/php/upload.php. Open that file in a text
    // editor to get a better idea of how it works.

    $.ajax({
        url: './assets/php/upload.php',
        data: fd,
        contentType:false,        // This will make the browser use the multipart/formdata encoding, which is required for transferring binary data.
        processData:false,        // jQuery shouldn't do any processsing on the data - the browser will handle this when it sees we are passing a formdata object. type:'POST', success: function(m){ log(m); } }); }); 复制代码

41.使用Facebook的图表

咱们能够引入facebook中的一个很强大的API来是咱们的app更加社交化。下面是一个简单的例子：

CODE
// Fetch the publicly accessible data on Tutorialzine's Page var api = 'http://graph.facebook.com/Tutorialzine/?callback=?', holder = $('#fbdata');


$.getJSON(api, function(r){

    // This will always give the current picture
    holder.append('<img src="http://graph.facebook.com/Tutorialzine/picture/?type=large">');

    holder.append('<p>'+ r.about +'</p>')
    holder.append('<a href="'+ r.website +'">'+ r.website +'</a>');

});
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42.获取天气信息

Open Weather Map提供了免费的天气信息，咱们能够经过使用它们的JSON API来获取数据。简单的例子以下：

// Request weather data:
var api = 'http://openweathermap.org/data/2.1/find/name?q=paris,france&callback=?';


$.getJSON(api, function(r){
    // This will always give the current picture
    log(r.list[0].name + ', ' + r.list[0].sys.country);
    log(r.list[0].main);

    // Temperatures are in kelvin, subtract 273.15 to convert to Celsius,
});
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43. 获取你的最近的汤博乐(Tumblr)内容

如今很是流行的汤博乐博客服务提供了简单的方法使用JSON api，这样咱们可使用它来获取任何博客内容，下面是使用的方法。

<div id="post"></div>
// Define variables
var blog = 'minimaldesks.tumblr.com',
    api  = 'http://' + blog + '/api/read/json?callback=?',
    post = $('#post');


$.getJSON(api, function(r){

    log('Blog title: ' + r.tumblelog.title);
    log('Description: ' + r.tumblelog.description);

    // If this post has a photo, show it
    if(r.posts[0]['photo-url-250']){
        post.append('<img src="' + r.posts[0]['photo-url-250'] + '" />');
    }
    else{
        log('Latest post: ' + r.posts[0]['regular-title']);
    }

});
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44.经过IP地址得到地理位置

有不少在线服务能够告诉咱们IP地址所在的城市和国家，下面咱们先ping到百度的IP地址，而后获取其地理位置：

// Define variables
var ip = '119.75.218.70', // you can optionally put an ip address here
    api  = 'http://freegeoip.net/json/' + ip + '?callback=?';


$.getJSON(api, function(r){

    console.log('How is the weather in ' + r.city + ', ' + r.country_name + '?');

}); //How is the weather in Beijing, China?
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45.使用YQL来爬网站

YQL对JavaScript开发者来讲有无限的API，下面的例子是咱们如何使用它来获取并解析其余站点的HTML。

CODE
// Define variables

var query = 'select * from data.html.cssselect where url="http://www.chucknorrisfacts.com/chuck-norris-top-50-facts" and css=".field-content a"';
var yqlAPI = 'http://query.yahooapis.com/v1/public/yql?q=' + encodeURIComponent(query) + ' &format=json&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=?';


$.getJSON(yqlAPI, function(r){

    log('Chuck Norris Facts:');

    $.each(r.query.results.results.a, function(){
        log('----------');
        log(this.content);
    });

});
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46.使用全局的Ajax方法

咱们能够经过ajax的全局方法来简化web app中处理的ajax请求。

CODE
// Create an indicator that would be shown whenever an AJAX request occurs:

var preloader = $('<div>',{ 'class':'preloader' }).appendTo('body');
var doc = $(document);

// Show the preloader whenever you are making an AJAX request:

doc.ajaxStart(function(){
    preloader.fadeIn();
});

// Hide it when the ajax request finishes

doc.ajaxComplete(function(){
    // Keep it visible for 0.8 seconds after the request completes
    preloader.delay(800).fadeOut();
});

// It will show automatically every time you do an AJAX request:

$.get('assets/misc/1.json');
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47. 学会爱上console吧。

咱们的浏览器给了咱们一系列有用的方法使用来调试代码，找出bug，下面就是一个例子，打开console看看吧。

// The simple case. Use this instead of alert():
console.log('This is a console message!');

// It supports embedding of variables as well:
var a = 'morning', b = 'Miss';
console.log('Good %s %s! How are you feeling today?', a, b);

// Interactively browse the properties of a method (similar to console.log):
console.dir(window);

// Information message (in webkit it looks like console.log)
console.info('Everything is OK');

// Warning message
console.warn('Something may be wrong');

// Error message (will print a stack trace)
console.error('Ooops. That was bad.');

// Counting things
for(var i = 0; i<20; i++){
    console.count('Counter Name');
}

// Starts a collapsable group of log messages
console.group("Preflight check");
console.info('Fuel is OK');
console.info('Temperature is normal');
console.error('Wings are missing');
console.groupEnd()

// Timing things
console.time('The million-dollar loop')

var dollars = 0;

for(var i=0;i<100000; i++){
    dollars+=10;
}

console.timeEnd('The million-dollar loop');

// Profiling code (it will show up in your console's Profile tab) console.profile('My app performance'); var arr = []; $.each([0,1,2,3,4,5,6,7,8,9],function(){ arr.push(this+1); }); console.profileEnd('My app performance'); 复制代码

48.把代码转化为插件以提升重用率。

若是有一些代码你老是在不一样的项目之间复制粘贴，你就能够考虑着把它转化成一个插件了。下面的例子就是这样。

<input id="testInput" placeholder="YourName"/>
     <script src="http://code.jquery.com/jquery-1.10.2.min.js"></script>

     <script>
// Define the placeholder plugin

$.fn.placeholder = function(){

    if ('placeholder' in document.createElement('input')){

        // This browser already supports placeholders.
        // Nothing to do here.
        return this;
    }

    this.each(function(){
        var input = $(this);

        input.on('focus', function(){

            if(input.val() == input.attr('placeholder')){

                input.val('');
            }

        }).on('blur', function(){

            if(input.val() == ''){
                input.val(input.attr('placeholder'));
            }

        });

        // Show the placeholder on load
        input.trigger('blur');
    });

    return this;
};

// And here is how to use it:
$('#testInput').placeholder();
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49.使用匿名函数来产生一个独立的代码块

定义全局变量和函数是一种代码很粗糙的行为，更好的方式是经过使用匿名函数使你的代码独立于块之中。看下面的例子：

// Isolating a block of code:

(function($){

    // Declare a variable. It will only be visible in this block.
    var c = 1;

    // Define a simple plugin

    $.fn.count = function(){

        // Increment and log the counter
        log(c++);

        return this;
    };

})(jQuery);

// The c variable is only visible for the plugin and will keep
// its value between invocations:

$(document).count();

$('body').count().count();
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50. 用extend融合对象

当提到从多个项目到一个项目结合属性时，你最好的猜想就是扩展方法。

// Combine properties (useful in plugins).
// The defaults are passed as the first argument.

var supplied = { height: 400 };

var options = $.extend({
    color    : 'blue',
    width    : 200,
    height    : 150
}, supplied);

log('New options:', options);

// You can also pass more than one object

log('Three parents:', $.extend({a:2}, {b:3}, {c:4}) );

log('-------');


// Cloning objects.
// To clone an object, simply pass an empty one
// as the first argument

var original = {a:123, b:'#fff'};
var clone = $.extend({}, original);

log('Clone:', clone);

log('-------');


// Extending jQuery.
// You can define plugins with extend

$.extend($.fn, {
    plugin1: function(){
        log('Plugin 1');
        return this;
    },
    plugin2: function(){
        log('Plugin 2');
        return this;
    }
});

$('body').plugin1().plugin2();

log('-------');

// If you pass only one arguments to $.extend,
// it will add the properties to the jQuery object

$.extend({ dontDoThis : 123});

log($.dontDoThis);

log('-------');

// Deep cloning.
// If you have nested objects, you will have to
// pass one additional argument to extend:

var obj1 = { a: 1, b: 2, c: {d: 3} };
var obj2 = { c: {e: 4}, f:5};

// This won't work // $.extend(obj1, obj2); // This will $.extend(true, obj1,obj2); log('Deep clone:', obj1); 复制代码