【譯】jQuery的50個使用技巧

時間 2019-11-17

標籤 jquery 使用技巧欄目 JQuery 简体版

原文原文鏈接

1.當document文檔就緒時執行JavaScript代碼。

<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> 複製代碼

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邊的表達式是false，那麼它就不會再判斷操做符右邊的表達式了。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()方法比你想象的更爲強大。

下面舉幾個例子，咱們先寫一個id爲elem的div。js代碼以下：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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其中判斷是否爲動畫我以爲很是不錯。html

5.判斷你的網頁一共有多少元素。

經過使用$("*").length屬性能夠判斷網頁的元素數量。jquery

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

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

// Trickshot:

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

log($('#elem').exists() ? "exists!" : "doesn't exist!");
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7.jQuery方法$()其實是擁有兩個參數的，你知道第二個參數的做用嗎？

// 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咱們能夠判斷一個連接是不是外部的，並來添加一個icon在非外部連接中，且肯定打開方式。

這裏用到了hostname屬性。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鏈更加高效。

<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.也許你但願你的web 應用感受更像原生的，那麼你能夠阻止contextmenu默認事件。

<script>
    // Prevent right clicking on this page
    $(function(){
        $(document).on("contextmenu",function(e){
            e.preventDefault();
        });
    });
</script>
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11.一些站點可能會使你的網頁在一個bar下面，即咱們所看到在下面的網頁是iframe標籤中的，咱們能夠這樣解決。

// 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.你的內聯樣式表並非被設置爲不可改變的，以下：

// Make the stylesheet visible and editable
$('#regular-style-block').css({'display':'block', 'white-space':'pre'})
                         .attr('contentEditable',true);
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這樣便可改變內聯樣式了。web

13.有時候咱們不但願網頁的某一部份內容被選擇好比複製粘貼這種事情，咱們能夠這麼作：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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這樣，內容就不能被選擇啦。正則表達式

14.從CDN中引入jQuery，這樣的方法能夠提升咱們網站的性能，而且引入最新的版本也是一個不錯的主意。

下面會介紹四種不一樣的方法。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> --> 複製代碼

15.保證最小的DOM操做。

咱們知道js操做DOM是很是浪費資源的，咱們能夠看看下面的例子。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。

也許你會使用正則表達式來解析URL，但這絕對不是一種好的方法，咱們能夠借用a標籤來實現它。

// 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.不要懼怕使用vanilla.js。

jQuery揹負的太多，這即是緣由，你能夠用通常的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); }); 複製代碼

18.最優化你的選擇器

// 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.緩存你的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.對於重複的函數只定義一次

若是你追求代碼的更高性能，那麼當你設置事件監聽程序時必須當心，只定義一次函數而後把它的名字做爲事件處理程序傳遞是不錯的方法。

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

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

});
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21.像對待數組同樣地對待jQuery對象

因爲jQuery對象有index值和長度，因此這意味着咱們能夠把對象看成普通的數組對待。這樣也會有更好地性能。

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.當作複雜的修改時要分離元素。

修改一個dom元素要求網頁重繪，這個代價是高昂的，因此若是你想要再提升性能，就能夠嘗試着當對一個元素進行大量修改時先從頁面中分離這個元素，修改完以後再添加到頁面。

// 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。

咱們已經習慣了把咱們全部的代碼都放在ready的事件處理程序中，可是，若是你的html頁面很龐大，decument ready恐怕會被延遲了，因此對於一些咱們不但願ready後才能夠觸發的事件能夠放在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.當使用js給多個元素添加樣式時更好的作法是建立一個style元素。

咱們以前提到過，操做dom是很是慢的，因此當添加多個元素的樣式時建立一個style元素並添加到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.給html元素分配一個名爲JS的class。

現代的web apps很是的依賴js，這裏的一個技巧就是隻有當js可用時才能顯示特定的元素。看下面的代碼。

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


html.JS #message { display:block; }
#message {display:none;}
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這樣，只有js可用的時候id爲message的元素纔會顯示；若是不支持js，則該元素不會顯示。

26.監聽不存在的元素上的事件。

jQuery擁有一個先進的事件處理機制，經過on()方法能夠監聽還不存在的事件。這是由於on方法能夠傳遞一個元素的子元素選擇器做爲參數。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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這樣，即便li是後建立的，也能夠經過on()方法來監聽。

27.只使用一次事件監聽。

有時，咱們只須要綁定只運行一次的事件處理程序。那麼one()方法是一個不錯的選擇，經過它你就能夠高枕無憂了。

<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.模擬觸發事件。

咱們能夠經過使用trigger模擬觸發一個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.使用觸摸事件。

使用觸摸事件和相關的鼠標事件並無太多不一樣，可是你得有一個方便的移動設備來測試會更好。看下面這個例子。

// 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版本時對事件處理進行了簡化，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.更快地阻止默認事件行爲。

咱們知道js中可使用preventDefault()方法來阻止默認行爲，可是jQuery對此提供了更簡單的方法。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連接多個事件處理程序。

對一個元素綁定多個事件處理程序並不常見，而使用event.result更能夠將多個事件處理程序聯繫起來。看下面的例子。

<button id="press">點擊</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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這樣，控制檯會輸出Hip Hop!

33.建立你本身習慣的事件。

你可使用on()方法建立本身喜歡的事件名稱，而後經過trigger來觸發。舉例以下：

<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.在下載文件旁顯示文件大小。

你知道如何在不下載一個文件的狀況下經過發送一個ajax請求頭獲得一個文件的大小嗎？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：這個例子如何咱們直接使用瀏覽器是無法獲得的，必須使用本地的web服務器打開運行才能夠。

35.使用延遲簡化你的Ajax請求

延遲(deferreds)是一個強大的工具。jQuery對於每個Ajax請求都會返回一個deferred對象。 deferred.done()方法接受一個或多個參數，全部這些都參數能夠是一個單一的函數或一個函數數組。當Deferred（延遲）解決時，doneCallbacks被調用。回調是依照他們添加的順序執行。一旦deferred.done()返回Deferred（延遲）對象，Deferred（延遲）能夠連接其它的延遲對象，包括增長額外的.done()方法。下面這樣就會使你的代碼更易讀：

// 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.平行的運行多個Ajax請求。

當咱們須要發送多個Ajax請求是，相反於等待一個發送結束再發送下一個，咱們能夠平行地發送來加速Ajax請求發送。

// 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.經過jQuery得到ip

咱們不只能夠在電腦上ping到一個網站的ip，也能夠經過jQuery獲得。

$.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); }); 複製代碼

38.使用最簡單的ajax請求

jQuery（使用ajax）提供了一個速記的方法來快速下載內容並添加在一個元素中。

<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.序列化對象

jQuery提供了一個方法序列化表單值和通常的對象成爲URL編碼文本字符串。這樣，咱們就能夠把序列化的值傳給ajax()做爲url的參數，輕鬆使用ajax()提交表單了。

<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上傳二進制文件

如今的瀏覽器都支持FormData API，這能夠是咱們很輕鬆的經過ajax來發送數據。並將之結合HTML5中的File API，咱們就能夠上傳二進制文件了。

// 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); } }); }); 複製代碼

41.使用Facebook的圖表

咱們能夠引入facebook中的一個很強大的API來是咱們的app更加社交化。下面是一個簡單的例子：

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.獲取天氣信息

Open Weather Map提供了免費的天氣信息，咱們能夠經過使用它們的JSON API來獲取數據。簡單的例子以下：

// 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. 獲取你的最近的湯博樂(Tumblr)內容

如今很是流行的湯博樂博客服務提供了簡單的方法使用JSON api，這樣咱們可使用它來獲取任何博客內容，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.經過IP地址得到地理位置

有不少在線服務能夠告訴咱們IP地址所在的城市和國家，下面咱們先ping到百度的IP地址，而後獲取其地理位置：

// 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來爬網站

YQL對JavaScript開發者來講有無限的API，下面的例子是咱們如何使用它來獲取並解析其餘站點的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

咱們能夠經過ajax的全局方法來簡化web app中處理的ajax請求。

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. 學會愛上console吧。

咱們的瀏覽器給了咱們一系列有用的方法使用來調試代碼，找出bug，下面就是一個例子，打開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'); 複製代碼

48.把代碼轉化爲插件以提升重用率。

若是有一些代碼你老是在不一樣的項目之間複製粘貼，你就能夠考慮着把它轉化成一個插件了。下面的例子就是這樣。

<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.使用匿名函數來產生一個獨立的代碼塊

定義全局變量和函數是一種代碼很粗糙的行爲，更好的方式是經過使用匿名函數使你的代碼獨立於塊之中。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融合對象

當提到從多個項目到一個項目結合屬性時，你最好的猜想就是擴展方法。

// 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); 複製代碼

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